POSTCONF(5)                                                        POSTCONF(5)



NAME
       postconf - Postfix configuration parameters

SYNOPSIS
       postconf parameter ...

       postconf -e "parameter=value" ...

DESCRIPTION
       The  Postfix  main.cf configuration file specifies parameters that con-
       trol the operation of the Postfix mail system. Typically the file  con-
       tains  only  a small subset of all parameters; parameters not specified
       are left at their default values.

       The general format of the main.cf file is as follows:

             Each logical line has the form "parameter = value".   Whitespace
              around the "=" is ignored, as is whitespace at the end of a log-
              ical line.

             Empty lines and whitespace-only lines are ignored, as are  lines
              whose first non-whitespace character is a `#'.

             A  logical  line  starts  with  non-whitespace text. A line that
              starts with whitespace continues a logical line.

             A parameter value may refer to other parameters.

                    The expressions "$name"  and  "${name}"  are  recursively
                     replaced  with the value of the named parameter. An unde-
                     fined parameter value is replaced with the empty value.

                    The expressions "${name?value}" and "${name?{value}}" are
                     replaced  with  "value"  when "$name" is non-empty. These
                     forms are supported with Postfix versions >= 2.2  and  >=
                     3.0, respectively.

                    The expressions "${name:value}" and "${name:{value}}" are
                     replaced with "value" when "$name" is empty. These  forms
                     are  supported  with  Postfix versions >= 2.2 and >= 3.0,
                     respectively.

                    The expression  "${name?{value1}:{value2}}"  is  replaced
                     with   "value1"  when  "$name"  is  non-empty,  and  with
                     "value2" when "$name" is empty.  The "{}" is required for
                     "value1",  optional  for "value2". This form is supported
                     with Postfix versions >= 3.0.

                    The first item inside "${...}" may be a  logical  expres-
                     sion  of  the  form:  "{value3} == {value4}". Besides the
                     "==" (equality) operator Postfix supports "!="  (inequal-
                     ity), "<", "<=", ">=", and ">". The comparison is numeri-
                     cal when both operands are all digits, otherwise the com-
                     parison  is  lexicographical.  These  forms are supported
                     with Postfix versions >= 3.0.

                    Each "value" is subject to recursive named parameter  and
                     logical expression evaluation, except where noted.

                    Whitespace before or after each "{value}" is ignored.

                    Specify "$$" to produce a single "$" character.

                    The  legacy  form "$(...)" is equivalent to the preferred
                     form "${...}".

             When the same parameter is defined multiple times, only the last
              instance is remembered.

             Otherwise,  the  order of main.cf parameter definitions does not
              matter.

       The remainder of this document is a description of all Postfix configu-
       ration parameters. Default values are shown after the parameter name in
       parentheses, and can be looked up with the "postconf -d" command.

       Note: this is not an invitation to make changes to  Postfix  configura-
       tion  parameters.  Unnecessary  changes can impair the operation of the
       mail system.

2bounce_notice_recipient (default: postmaster)
       The recipient of undeliverable mail that  cannot  be  returned  to  the
       sender.  This feature is enabled with the notify_classes parameter.

access_map_defer_code (default: 450)
       The  numerical  Postfix  SMTP server response code for an access(5) map
       "defer" action, including "defer_if_permit" or "defer_if_reject". Prior
       to Postfix 2.6, the response is hard-coded as "450".

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

       This feature is available in Postfix 2.6 and later.

access_map_reject_code (default: 554)
       The numerical Postfix SMTP server response code for  an  access(5)  map
       "reject" action.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

address_verify_cache_cleanup_interval (default: 12h)
       The amount of time  between  verify(8)  address  verification  database
       cleanup  runs.  This  feature  requires  that the database supports the
       "delete" and "sequence" operators.  Specify a zero interval to  disable
       database cleanup.

       After  each  database cleanup run, the verify(8) daemon logs the number
       of entries that were retained and dropped. A cleanup run is  logged  as
       "partial"  when  the  daemon  terminates  early after "postfix reload",
       "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.7.

address_verify_default_transport (default: $default_transport)
       Overrides the default_transport parameter setting for address verifica-
       tion probes.

       This feature is available in Postfix 2.1 and later.

address_verify_local_transport (default: $local_transport)
       Overrides  the  local_transport parameter setting for address verifica-
       tion probes.

       This feature is available in Postfix 2.1 and later.

address_verify_map (default: see postconf -d output)
       Lookup table for persistent address verification status  storage.   The
       table  is maintained by the verify(8) service, and is opened before the
       process releases privileges.

       The lookup table is persistent by  default  (Postfix  2.7  and  later).
       Specify  an empty table name to keep the information in volatile memory
       which is lost after "postfix reload" or "postfix  stop".  This  is  the
       default with Postfix version 2.6 and earlier.

       Specify a location in a file system that will not fill up. If the data-
       base becomes corrupted, the world comes to an end.  To  recover  delete
       (NOT: truncate) the file and do "postfix reload".

       Postfix  daemon  processes do not use root privileges when opening this
       file (Postfix 2.5 and later).  The file must therefore be stored  under
       a  Postfix-owned  directory such as the data_directory.  As a migration
       aid, an attempt to open the file under a non-Postfix directory is redi-
       rected to the Postfix-owned data_directory, and a warning is logged.

       Examples:

       address_verify_map = hash:/var/db/postfix/verify
       address_verify_map = btree:/var/db/postfix/verify

       This feature is available in Postfix 2.1 and later.

address_verify_negative_cache (default: yes)
       Enable caching of failed address verification probe results.  When this
       feature is enabled, the cache may pollute quickly with  garbage.   When
       this  feature  is  disabled, Postfix will generate an address probe for
       every lookup.

       This feature is available in Postfix 2.1 and later.

address_verify_negative_expire_time (default: 3d)
       The time after which a failed probe expires from the address  verifica-
       tion cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_negative_refresh_time (default: 3h)
       The  time  after  which a failed address verification probe needs to be
       refreshed.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_pending_request_limit (default: see postconf -d output)
       A safety limit that prevents address verification requests  from  over-
       whelming  the Postfix queue. By default, the number of pending requests
       is  limited  to  1/4  of  the  active  queue  maximum  size  (qmgr_mes-
       sage_active_limit). The queue manager enforces the limit by tempfailing
       requests that exceed the limit. This affects only unknown addresses and
       inactive  addresses  that  have  expired,  because the verify(8) daemon
       automatically refreshes an active address before it expires.

       This feature is available in Postfix 3.1 and later.

address_verify_poll_count (default: normal: 3, overload: 1)
       How many times to query the verify(8) service for the completion of  an
       address verification request in progress.

       By  default,  the Postfix SMTP server polls the verify(8) service up to
       three times under non-overload conditions, and  only  once  when  under
       overload.  With Postfix version 2.5 and earlier, the SMTP server always
       polls the verify(8) service up to three times by default.

       Specify 1 to implement a crude form of  greylisting,  that  is,  always
       defer the first delivery request for a new address.

       Examples:

       # Postfix <= 2.6 default
       address_verify_poll_count = 3
       # Poor man's greylisting
       address_verify_poll_count = 1

       This feature is available in Postfix 2.1 and later.

address_verify_poll_delay (default: 3s)
       The delay between queries for the completion of an address verification
       request in progress.

       The default polling delay is 3 seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_expire_time (default: 31d)
       The time after which a successful probe expires from the address  veri-
       fication cache.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_positive_refresh_time (default: 7d)
       The  time  after which a successful address verification probe needs to
       be refreshed.  The address verification status is not updated when  the
       probe fails (optimistic caching).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.1 and later.

address_verify_relay_transport (default: $relay_transport)
       Overrides  the  relay_transport parameter setting for address verifica-
       tion probes.

       This feature is available in Postfix 2.1 and later.

address_verify_relayhost (default: $relayhost)
       Overrides the relayhost  parameter  setting  for  address  verification
       probes.  This information can be overruled with the transport(5) table.

       This feature is available in Postfix 2.1 and later.

address_verify_sender (default: $double_bounce_sender)
       The sender address to use in  address  verification  probes;  prior  to
       Postfix  2.5  the  default  was  "postmaster".  To  avoid problems with
       address probes that are sent in response to address probes, the Postfix
       SMTP  server  excludes  the  probe sender address from all SMTPD access
       blocks.

       Specify an empty value (address_verify_sender =) or <> if you  want  to
       use  the  null  sender address. Beware, some sites reject mail from <>,
       even though RFCs require that such addresses be accepted.

       Examples:

       address_verify_sender = <>
       address_verify_sender = postmaster@my.domain

       This feature is available in Postfix 2.1 and later.

address_verify_sender_dependent_default_transport_maps               (default:
       $sender_dependent_default_transport_maps)
       Overrides the sender_dependent_default_transport_maps parameter setting
       for address verification probes.

       This feature is available in Postfix 2.7 and later.

address_verify_sender_dependent_relayhost_maps    (default:     $sender_depen-
       dent_relayhost_maps)
       Overrides  the  sender_dependent_relayhost_maps  parameter  setting for
       address verification probes.

       This feature is available in Postfix 2.3 and later.

address_verify_sender_ttl (default: 0s)
       The time between changes in the time-dependent portion of address veri-
       fication probe sender addresses. The time-dependent portion is appended
       to the  localpart  of  the  address  specified  with  the  address_ver-
       ify_sender  parameter.  This  feature  is ignored when the probe sender
       addresses is the null sender, i.e. the address_verify_sender  value  is
       empty or <>.

       Historically,  the probe sender address was fixed. This has caused such
       addresses to end up on spammer  mailing  lists,  and  has  resulted  in
       wasted network and processing resources.

       To  enable  time-dependent  probe  sender addresses, specify a non-zero
       time value (an integral value plus an optional one-letter  suffix  that
       specifies  the  time unit).  Specify a value of at least several hours,
       to avoid problems with senders that use greylisting.   Avoid  nice  TTL
       values,  to  make the result less predictable.  Time units are: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.9 and later.

address_verify_service_name (default: verify)
       The name of the verify(8) address verification  service.  This  service
       maintains  the  status  of sender and/or recipient address verification
       probes, and generates probes on request by other Postfix processes.

address_verify_transport_maps (default: $transport_maps)
       Overrides the transport_maps parameter setting for address verification
       probes.

       This feature is available in Postfix 2.1 and later.

address_verify_virtual_transport (default: $virtual_transport)
       Overrides the virtual_transport parameter setting for address verifica-
       tion probes.

       This feature is available in Postfix 2.1 and later.

alias_database (default: see postconf -d output)
       The alias  databases  for  local(8)  delivery  that  are  updated  with
       "newaliases" or with "sendmail -bi".

       This  is  a separate configuration parameter because not all the tables
       specified with $alias_maps have to be local files.

       Examples:

       alias_database = hash:/etc/aliases
       alias_database = hash:/etc/mail/aliases

alias_maps (default: see postconf -d output)
       The alias databases that are used for local(8) delivery. See aliases(5)
       for  syntax  details.   Specify zero or more "type:name" lookup tables,
       separated by whitespace or comma. Tables will be searched in the speci-
       fied  order until a match is found.  Note: these lookups are recursive.

       The default list is system dependent.  On systems with NIS, the default
       is to search the local alias database, then the NIS alias database.

       If  you  change  the  alias  database, run "postalias /etc/aliases" (or
       wherever your system  stores  the  mail  alias  file),  or  simply  run
       "newaliases" to build the necessary DBM or DB file.

       The  local(8)  delivery agent disallows regular expression substitution
       of $1 etc. in alias_maps, because that would open a security hole.

       The local(8) delivery agent will silently ignore requests  to  use  the
       proxymap(8)  server  within  alias_maps. Instead it will open the table
       directly. Before Postfix version 2.2, the local(8) delivery agent  will
       terminate with a fatal error.

       Examples:

       alias_maps = hash:/etc/aliases, nis:mail.aliases
       alias_maps = hash:/etc/aliases

allow_mail_to_commands (default: alias, forward)
       Restrict  local(8)  mail delivery to external commands.  The default is
       to disallow delivery to "|command" in :include:  files (see  aliases(5)
       for the text that defines this terminology).

       Specify  zero  or more of: alias, forward or include, in order to allow
       commands in aliases(5), .forward files or in :include:  files,  respec-
       tively.

       Example:

       allow_mail_to_commands = alias,forward,include

allow_mail_to_files (default: alias, forward)
       Restrict  local(8)  mail  delivery to external files. The default is to
       disallow "/file/name" destinations in :include:  files (see  aliases(5)
       for the text that defines this terminology).

       Specify  zero  or more of: alias, forward or include, in order to allow
       "/file/name"  destinations  in  aliases(5),  .forward  files   and   in
       :include:  files, respectively.

       Example:

       allow_mail_to_files = alias,forward,include

allow_min_user (default: no)
       Allow a sender or recipient address to have `-' as the first character.
       By default, this is not allowed, to avoid accidents with software  that
       passes email addresses via the command line. Such software would not be
       able to distinguish a malicious address from a bona  fide  command-line
       option.  Although this can be prevented by inserting a "--" option ter-
       minator into the command line, this is  difficult  to  enforce  consis-
       tently and globally.

       As  of  Postfix version 2.5, this feature is implemented by trivial-re-
       write(8).  With  earlier  versions  this  feature  was  implemented  by
       qmgr(8) and was limited to recipient addresses only.

allow_percent_hack (default: yes)
       Enable  the rewriting of the form "user%domain" to "user@domain".  This
       is enabled by default.

       Note: as of Postfix version 2.2, message header address rewriting  hap-
       pens only when one of the following conditions is true:

             The message is received with the Postfix sendmail(1) command,

             The  message  is  received  from  a  network client that matches
              $local_header_rewrite_clients,

             The  message   is   received   from   the   network,   and   the
              remote_header_rewrite_domain  parameter  specifies  a  non-empty
              value.

       To   get   the   behavior   before   Postfix   version   2.2,   specify
       "local_header_rewrite_clients = static:all".

       Example:

       allow_percent_hack = no

allow_untrusted_routing (default: no)
       Forward  mail  with sender-specified routing (user[@%!]remote[@%!]site)
       from untrusted clients to destinations matching $relay_domains.

       By default, this feature is turned off.  This closes a nasty open relay
       loophole  where  a  backup  MX host can be tricked into forwarding junk
       mail to a primary MX host which then spams it out to the world.

       This parameter also controls if non-local addresses with  sender-speci-
       fied  routing  can  match  Postfix  access  tables.  By  default,  such
       addresses cannot match Postfix access tables, because  the  address  is
       ambiguous.

alternate_config_directories (default: empty)
       A  list  of  non-default  Postfix configuration directories that may be
       specified with "-c config_directory" on the command line,  or  via  the
       MAIL_CONFIG environment parameter.

       This list must be specified in the default Postfix configuration direc-
       tory, and is used by set-gid Postfix commands such as postqueue(1)  and
       postdrop(1).

always_add_missing_headers (default: no)
       Always  add (Resent-) From:, To:, Date: or Message-ID: headers when not
       present.  Postfix 2.6 and later add these  headers  only  when  clients
       match  the  local_header_rewrite_clients  parameter  setting.   Earlier
       Postfix versions always add these headers; this may break  DKIM  signa-
       tures   that   cover  non-existent  headers.   The  undisclosed_recipi-
       ents_header parameter setting determines whether a To: header  will  be
       added.

always_bcc (default: empty)
       Optional  address  that  receives a "blind carbon copy" of each message
       that is received by the Postfix mail system.

       Note: with Postfix 2.3 and later the BCC address is added as if it  was
       specified  with  NOTIFY=NONE.  The sender will not be notified when the
       BCC address is undeliverable,  as  long  as  all  down-stream  software
       implements RFC 3461.

       Note: with Postfix 2.2 and earlier the sender will be notified when the
       BCC address is undeliverable.

       Note: automatic BCC recipients are produced  only  for  new  mail.   To
       avoid  mailer  loops,  automatic BCC recipients are not generated after
       Postfix forwards mail  internally,  or  after  Postfix  generates  mail
       itself.

anvil_rate_time_unit (default: 60s)
       The  time  unit  over which client connection rates and other rates are
       calculated.

       This feature is implemented by the anvil(8) service which is  available
       in Postfix version 2.2 and later.

       The default interval is relatively short. Because of the high frequency
       of updates, the anvil(8) server uses volatile memory only. Thus, infor-
       mation is lost whenever the process terminates.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

anvil_status_update_time (default: 600s)
       How frequently the anvil(8) connection and rate  limiting  server  logs
       peak usage information.

       This feature is available in Postfix 2.2 and later.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

append_at_myorigin (default: yes)
       With locally submitted mail, append the  string  "@$myorigin"  to  mail
       addresses  without  domain  information.  With remotely submitted mail,
       append the string "@$remote_header_rewrite_domain" instead.

       Note 1: this feature is enabled by default and must not be turned  off.
       Postfix does not support domain-less addresses.

       Note 2: with Postfix version 2.2, message header address rewriting hap-
       pens only when one of the following conditions is true:

             The message is received with the Postfix sendmail(1) command,

             The message is received  from  a  network  client  that  matches
              $local_header_rewrite_clients,

             The   message   is   received   from   the   network,   and  the
              remote_header_rewrite_domain  parameter  specifies  a  non-empty
              value.

       To   get   the   behavior   before   Postfix   version   2.2,   specify
       "local_header_rewrite_clients = static:all".

append_dot_mydomain (default: Postfix >= 3.0: no, Postfix < 3.0: yes)
       With  locally  submitted  mail,  append  the  string  ".$mydomain"   to
       addresses  that  have no ".domain" information. With remotely submitted
       mail, append the string ".$remote_header_rewrite_domain" instead.

       Note 1: this feature is enabled by default. If disabled, users will not
       be able to send mail to "user@partialdomainname" but will have to spec-
       ify full domain names instead.

       Note 2: with Postfix version 2.2, message header address rewriting hap-
       pens only when one of the following conditions is true:

             The message is received with the Postfix sendmail(1) command,

             The  message  is  received  from  a  network client that matches
              $local_header_rewrite_clients,

             The  message   is   received   from   the   network,   and   the
              remote_header_rewrite_domain  parameter  specifies  a  non-empty
              value.

       To   get   the   behavior   before   Postfix   version   2.2,   specify
       "local_header_rewrite_clients = static:all".

application_event_drain_time (default: 100s)
       How long the postkick(1) command waits for a request to enter the Post-
       fix daemon process input buffer before giving up.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

authorized_flush_users (default: static:anyone)
       List of users who are authorized to flush the queue.

       By default, all users are allowed to flush the queue.  Access is always
       granted if the invoking user is the super-user or the $mail_owner user.
       Otherwise, the real UID of the process is looked up in the system pass-
       word file, and access is granted only if the corresponding  login  name
       is  on  the  access list.  The username "unknown" is used for processes
       whose real UID is not found in the password file.

       Specify a list of user names, "/file/name"  or  "type:table"  patterns,
       separated  by  commas  and/or  whitespace.  The list is matched left to
       right, and the search stops on the first match. A "/file/name"  pattern
       is  replaced  by  its  contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).   Con-
       tinue  long  lines  by  starting the next line with whitespace. Specify
       "!pattern" to exclude a name from the list. The form  "!/file/name"  is
       supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_mailq_users (default: static:anyone)
       List of users who are authorized to view the queue.

       By  default, all users are allowed to view the queue.  Access is always
       granted if the invoking user is the super-user or the $mail_owner user.
       Otherwise, the real UID of the process is looked up in the system pass-
       word file, and access is granted only if the corresponding  login  name
       is  on  the  access list.  The username "unknown" is used for processes
       whose real UID is not found in the password file.

       Specify a list of user names, "/file/name"  or  "type:table"  patterns,
       separated  by  commas  and/or  whitespace.  The list is matched left to
       right, and the search stops on the first match. A "/file/name"  pattern
       is  replaced  by  its  contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).   Con-
       tinue  long  lines  by  starting the next line with whitespace. Specify
       "!pattern" to exclude a user name from the list. The form "!/file/name"
       is supported only in Postfix version 2.4 and later.

       This feature is available in Postfix 2.2 and later.

authorized_submit_users (default: static:anyone)
       List  of  users  who are authorized to submit mail with the sendmail(1)
       command (and with the privileged postdrop(1) helper command).

       By default, all users are allowed to submit mail.  Otherwise, the  real
       UID of the process is looked up in the system password file, and access
       is granted only if the corresponding login name is on the access  list.
       The  username  "unknown"  is  used  for processes whose real UID is not
       found in the password file. To deny mail submission access to all users
       specify an empty list.

       Specify  a  list  of user names, "/file/name" or "type:table" patterns,
       separated by commas and/or whitespace. The  list  is  matched  left  to
       right,  and the search stops on the first match. A "/file/name" pattern
       is replaced by its contents; a "type:table"  lookup  table  is  matched
       when  a name matches a lookup key (the lookup result is ignored).  Con-
       tinue long lines by starting the next  line  with  whitespace.  Specify
       "!pattern" to exclude a user name from the list. The form "!/file/name"
       is supported only in Postfix version 2.4 and later.

       Example:

       authorized_submit_users = !www, static:all

       This feature is available in Postfix 2.2 and later.

authorized_verp_clients (default: $mynetworks)
       What remote SMTP clients are allowed  to  specify  the  XVERP  command.
       This  command  requests  that mail be delivered one recipient at a time
       with a per recipient return address.

       By default, only trusted clients are allowed to specify XVERP.

       This parameter was introduced with Postfix version 1.1.   Postfix  ver-
       sion  2.1  renamed  this parameter to smtpd_authorized_verp_clients and
       changed the default to none.

       Specify a list of network/netmask patterns, separated by commas  and/or
       whitespace.  The  mask specifies the number of bits in the network part
       of a host address. You can also specify hostnames or .domain names (the
       initial   dot   causes   the  domain  to  match  any  name  below  it),
       "/file/name" or  "type:table"  patterns.   A  "/file/name"  pattern  is
       replaced by its contents; a "type:table" lookup table is matched when a
       table entry matches a lookup string (the  lookup  result  is  ignored).
       Continue  long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude an address or network block from  the  list.  The
       form  "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside  []  in
       the   authorized_verp_clients   value,  and  in  files  specified  with
       "/file/name".  IP version 6 addresses contain the  ":"  character,  and
       would otherwise be confused with a "type:table" pattern.

backwards_bounce_logfile_compatibility (default: yes)
       Produce  additional bounce(8) logfile records that can be read by Post-
       fix versions before 2.0. The current and more extensible "name = value"
       format  is  needed in order to implement more sophisticated functional-
       ity.

       This feature is available in Postfix 2.1 and later.

berkeley_db_create_buffer_size (default: 16777216)
       The per-table I/O buffer size for programs that create Berkeley DB hash
       or btree tables.  Specify a byte count.

       This feature is available in Postfix 2.0 and later.

berkeley_db_read_buffer_size (default: 131072)
       The  per-table  I/O buffer size for programs that read Berkeley DB hash
       or btree tables.  Specify a byte count.

       This feature is available in Postfix 2.0 and later.

best_mx_transport (default: empty)
       Where the Postfix SMTP client should deliver mail  when  it  detects  a
       "mail  loops  back  to  myself"  error condition. This happens when the
       local MTA is the best SMTP mail exchanger for a destination not  listed
       in    $mydestination,    $inet_interfaces,   $proxy_interfaces,   $vir-
       tual_alias_domains, or $virtual_mailbox_domains.  By default, the Post-
       fix SMTP client returns such mail as undeliverable.

       Specify, for example, "best_mx_transport = local" to pass the mail from
       the Postfix SMTP client to the local(8) delivery agent. You can specify
       any message delivery "transport" or "transport:nexthop" that is defined
       in the master.cf file. See the transport(5) manual page for the  syntax
       and meaning of "transport" or "transport:nexthop".

       However,  this  feature  is expensive because it ties up a Postfix SMTP
       client process while the local(8) delivery agent is doing its work.  It
       is  more  efficient (for Postfix) to list all hosted domains in a table
       or database.

biff (default: yes)
       Whether or not to use the local biff service.  This service sends  "new
       mail"  notifications  to users who have requested new mail notification
       with the UNIX command "biff y".

       For compatibility reasons this feature is on by  default.   On  systems
       with  lots  of interactive users, the biff service can be a performance
       drain.  Specify "biff = no" in main.cf to disable.

body_checks (default: empty)
       Optional lookup tables for  content  inspection  as  specified  in  the
       body_checks(5) manual page.

       Note: with Postfix versions before 2.0, these rules inspect all content
       after the primary message headers.

body_checks_size_limit (default: 51200)
       How much text in a message body segment (or attachment, if  you  prefer
       to  use  that term) is subjected to body_checks inspection.  The amount
       of text is limited to avoid scanning huge attachments.

       This feature is available in Postfix 2.0 and later.

bounce_notice_recipient (default: postmaster)
       The recipient of postmaster notifications with the message  headers  of
       mail  that Postfix did not deliver and of SMTP conversation transcripts
       of mail that Postfix did not receive.  This feature is enabled with the
       notify_classes parameter.

bounce_queue_lifetime (default: 5d)
       Consider  a bounce message as undeliverable, when delivery fails with a
       temporary  error,  and  the  time  in  the  queue   has   reached   the
       bounce_queue_lifetime limit.  By default, this limit is the same as for
       regular mail.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is d (days).

       Specify 0 when mail delivery should be tried only once.

       This feature is available in Postfix 2.1 and later.

bounce_service_name (default: bounce)
       The  name  of the bounce(8) service. This service maintains a record of
       failed delivery attempts and generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

bounce_size_limit (default: 50000)
       The maximal  amount  of  original  message  text  that  is  sent  in  a
       non-delivery notification. Specify a byte count.  A message is returned
       as   either   message/rfc822   (the   complete    original)    or    as
       text/rfc822-headers  (the  headers only).  With Postfix version 2.4 and
       earlier, a message is always returned as message/rfc822  and  is  trun-
       cated when it exceeds the size limit.

       Notes:

             If  you  increase  this  limit,  then  you  should  increase the
              mime_nesting_limit value proportionally.

             Be careful when making changes.  Excessively large  values  will
              result  in the loss of non-delivery notifications, when a bounce
              message size exceeds a local or remote MTA's message size limit.

bounce_template_file (default: empty)
       Pathname  of a configuration file with bounce message templates.  These
       override the built-in templates of delivery status  notification  (DSN)
       messages for undeliverable mail, for delayed mail, successful delivery,
       or delivery verification. The bounce(5) manual page  describes  how  to
       edit and test template files.

       Template message body text may contain $name references to Postfix con-
       figuration parameters. The result of $name expansion can  be  previewed
       with "postconf -b file_name" before the file is placed into the Postfix
       configuration directory.

       This feature is available in Postfix 2.3 and later.

broken_sasl_auth_clients (default: no)
       Enable interoperability with remote  SMTP  clients  that  implement  an
       obsolete  version  of  the  AUTH  command  (RFC 4954). Examples of such
       clients are MicroSoft Outlook Express version 4 and MicroSoft  Exchange
       version 5.0.

       Specify "broken_sasl_auth_clients = yes" to have Postfix advertise AUTH
       support in a non-standard way.

canonical_classes     (default:      envelope_sender,      envelope_recipient,
       header_sender, header_recipient)
       What  addresses  are  subject  to  canonical_maps  address mapping.  By
       default, canonical_maps address mapping is applied to  envelope  sender
       and  recipient  addresses,  and  to  header sender and header recipient
       addresses.

       Specify  one   or   more   of:   envelope_sender,   envelope_recipient,
       header_sender, header_recipient

       This feature is available in Postfix 2.2 and later.

canonical_maps (default: empty)
       Optional   address  mapping  lookup  tables  for  message  headers  and
       envelopes.  The  mapping  is  applied  to  both  sender  and  recipient
       addresses,  in  both  envelopes  and in headers, as controlled with the
       canonical_classes parameter. This is typically used to clean  up  dirty
       addresses from legacy mail systems, or to replace login names by First-
       name.Lastname.  The table format and lookups are documented in  canoni-
       cal(5).  For  an  overview  of  Postfix  address  manipulations see the
       ADDRESS_REWRITING_README document.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.  Note: these lookups are recursive.

       If you use this feature, run "postmap /etc/postfix/canonical" to  build
       the  necessary  DBM  or  DB  file  after every change. The changes will
       become visible after a minute or so.  Use "postfix reload" to eliminate
       the delay.

       Note:  with Postfix version 2.2, message header address mapping happens
       only when message header address rewriting is enabled:

             The message is received with the Postfix sendmail(1) command,

             The message is received  from  a  network  client  that  matches
              $local_header_rewrite_clients,

             The   message   is   received   from   the   network,   and  the
              remote_header_rewrite_domain  parameter  specifies  a  non-empty
              value.

       To   get   the   behavior   before   Postfix   version   2.2,   specify
       "local_header_rewrite_clients = static:all".

       Examples:

       canonical_maps = dbm:/etc/postfix/canonical
       canonical_maps = hash:/etc/postfix/canonical

cleanup_service_name (default: cleanup)
       The name of the cleanup(8) service.  This  service  rewrites  addresses
       into  the  standard form, and performs canonical(5) address mapping and
       virtual(5) aliasing.

       This feature is available in Postfix 2.0 and later.

command_directory (default: see postconf -d output)
       The location of all postfix administrative commands.

command_execution_directory (default: empty)
       The local(8) delivery agent working directory for delivery to  external
       command.   Failure  to  change  directory  causes  the  delivery  to be
       deferred.

       The following $name expansions are done on  command_execution_directory
       before  the  directory  is changed. Expansion happens in the context of
       the delivery request.  The result of $name expansion is  filtered  with
       the character set that is specified with the execution_directory_expan-
       sion_filter parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
              The full recipient address.

       $extension
              The optional recipient address extension.

       $domain
              The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
              The address extension delimiter that was found in the  recipient
              address  (Postfix  2.11 and later), or the system-wide recipient
              address extension delimiter (Postfix 2.10 and earlier).

       ${name?value}
              Expands to value when $name is non-empty.

       ${name:value}
              Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       This feature is available in Postfix 2.2 and later.

command_expansion_filter (default: see postconf -d output)
       Restrict the characters that the  local(8)  delivery  agent  allows  in
       $name  expansions of $mailbox_command and $command_execution_directory.
       Characters outside the allowed set are replaced by underscores.

command_time_limit (default: 1000s)
       Time limit for delivery to external commands. This limit is used by the
       local(8)  delivery agent, and is the default time limit for delivery by
       the pipe(8) delivery agent.

       Note: if you set this time limit to a large value you must  update  the
       global ipc_timeout parameter as well.

compatibility_level (default: 0)
       A  safety  net  that  causes  Postfix  to run with backwards-compatible
       default settings after an upgrade to a newer Postfix version.

       With backwards compatibility turned on (the main.cf compatibility_level
       value  is less than the Postfix built-in value), Postfix looks for set-
       tings that are left at their implicit default value, and logs a message
       when a backwards-compatible default setting is required.

           using backwards-compatible default setting name=value
               to [accept a specific client request]

           using backwards-compatible default setting name=value
               to [enable specific Postfix behavior]

       See  COMPATIBILITY_README  for specific message details. If such a mes-
       sage is logged in the context  of  a  legitimate  request,  the  system
       administrator should make the backwards-compatible setting permanent in
       main.cf or master.cf, for example:

           # postconf name=value
           # postfix reload

       When no more backwards-compatible settings need to be  made  permanent,
       the  administrator  should turn off backwards compatibility by updating
       the compatibility_level setting in main.cf:

           # postconf compatibility_level=N
           # postfix reload

       For N specify the number that is logged in your postfix(1) warning mes-
       sage:

           warning: To disable backwards compatibility use "postconf
               compatibility_level=N" and "postfix reload"

       This feature is available in Postfix 3.0 and later.

config_directory (default: see postconf -d output)
       The default location of the Postfix main.cf and master.cf configuration
       files. This can be overruled via the following mechanisms:

             The MAIL_CONFIG environment variable (daemon processes and  com-
              mands).

             The "-c" command-line option (commands only).

       With  Postfix command that run with set-gid privileges, a config_direc-
       tory override requires either root privileges, or it requires that  the
       directory  is listed with the alternate_config_directories parameter in
       the default main.cf file.

confirm_delay_cleared (default: no)
       After sending a "your message  is  delayed"  notification,  inform  the
       sender  when  the delay clears up. This can result in a sudden burst of
       notifications at the end of a prolonged network outage, and  is  there-
       fore disabled by default.

       See also: delay_warning_time.

       This feature is available in Postfix 3.0 and later.

connection_cache_protocol_timeout (default: 5s)
       Time  limit  for  connection cache connect, send or receive operations.
       The time limit is enforced in the client.

       This feature is available in Postfix 2.3 and later.

connection_cache_service_name (default: scache)
       The name of the scache(8) connection cache service.  This service main-
       tains a limited pool of cached sessions.

       This feature is available in Postfix 2.2 and later.

connection_cache_status_update_time (default: 600s)
       How  frequently the scache(8) server logs usage statistics with connec-
       tion cache hit and miss rates for logical destinations and for physical
       endpoints.

connection_cache_ttl_limit (default: 2s)
       The  maximal  time-to-live  value  that  the scache(8) connection cache
       server allows. Requests that specify a larger TTL will be  stored  with
       the  maximum  allowed TTL. The purpose of this additional control is to
       protect the infrastructure against careless people. The  cache  TTL  is
       already bounded by $max_idle.

content_filter (default: empty)
       After  the  message is queued, send the entire message to the specified
       transport:destination. The transport name specifies the first field  of
       a  mail  delivery  agent  definition  in  master.cf;  the syntax of the
       next-hop destination is described in the manual page of the correspond-
       ing delivery agent.  More information about external content filters is
       in the Postfix FILTER_README file.

       Notes:

             This setting has lower precedence than a FILTER action  that  is
              specified  in  an  access(5), header_checks(5) or body_checks(5)
              table.

             The meaning of an empty next-hop filter destination  is  version
              dependent.  Postfix 2.7 and later will use the recipient domain;
              earlier versions will use  $myhostname.   Specify  "default_fil-
              ter_nexthop = $myhostname" for compatibility with Postfix 2.6 or
              earlier, or specify a  content_filter  value  with  an  explicit
              next-hop destination.

cyrus_sasl_config_path (default: empty)
       Search  path  for Cyrus SASL application configuration files, currently
       used only to locate the $smtpd_sasl_path.conf file.   Specify  zero  or
       more  directories  separated by a colon character, or an empty value to
       use Cyrus SASL's built-in search path.

       This feature is available in Postfix 2.5 and later when  compiled  with
       Cyrus SASL 2.1.22 or later.

daemon_directory (default: see postconf -d output)
       The directory with Postfix support programs and daemon programs.  These
       should not be invoked directly by humans. The directory must  be  owned
       by root.

daemon_table_open_error_is_fatal (default: no)
       How  a  Postfix  daemon  process  handles  errors  while opening lookup
       tables: gradual degradation or immediate termination.

        no  (default)
              Gradual degradation: a daemon process logs  a  message  of  type
              "error" and continues execution with reduced functionality. Fea-
              tures that do not depend on the unavailable table will work nor-
              mally,  while features that depend on the table will result in a
              type "warning" message.
              When the notify_classes  parameter  value  contains  the  "data"
              class,  the  Postfix  SMTP  server  and client will report tran-
              scripts of sessions with an error because a  table  is  unavail-
              able.

        yes  (historical behavior)
              Immediate termination: a daemon process logs a type "fatal" mes-
              sage and terminates immediately.  This option reduces the number
              of  possible  code  paths  through Postfix, and may therefore be
              slightly more secure than the default.

       For the sake of sanity, the number of type "error" messages is  limited
       to 13 over the lifetime of a daemon process.

       This feature is available in Postfix 2.9 and later.

daemon_timeout (default: 18000s)
       How  much  time  a  Postfix daemon process may take to handle a request
       before it is terminated by a built-in watchdog timer.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

data_directory (default: see postconf -d output)
       The  directory  with  Postfix-writable data files (for example: caches,
       pseudo-random numbers).  This directory must be owned by the mail_owner
       account, and must not be shared with non-Postfix software.

       This feature is available in Postfix 2.5 and later.

debug_peer_level (default: 2)
       The  increment  in verbose logging level when a remote client or server
       matches a pattern in the debug_peer_list parameter.

debug_peer_list (default: empty)
       Optional list of remote client or server hostname  or  network  address
       patterns that cause the verbose logging level to increase by the amount
       specified in $debug_peer_level.

       Specify domain names, network/netmask patterns,  "/file/name"  patterns
       or   "type:table"  lookup  tables.  The  right-hand  side  result  from
       "type:table" lookups is ignored.

       Pattern matching of domain names  is  controlled  by  the  presence  or
       absence  of  "debug_peer_list"  in the parent_domain_matches_subdomains
       parameter value.

       Examples:

       debug_peer_list = 127.0.0.1
       debug_peer_list = example.com

debugger_command (default: empty)
       The external command to  execute  when  a  Postfix  daemon  program  is
       invoked with the -D option.

       Use  "command  .. & sleep 5" so that the debugger can attach before the
       process marches on. If you use an X-based debugger, be sure to  set  up
       your XAUTHORITY environment variable before starting Postfix.

       Note: the command is subject to $name expansion, before it is passed to
       the default command interpreter. Specify "$$" to produce a  single  "$"
       character.

       Example:

       debugger_command =
           PATH=/usr/bin:/usr/X11R6/bin
           ddd $daemon_directory/$process_name $process_id & sleep 5

default_database_type (default: see postconf -d output)
       The  default  database  type for use in newaliases(1), postalias(1) and
       postmap(1) commands. On many UNIX systems the default  type  is  either
       dbm  or  hash. The default setting is frozen when the Postfix system is
       built.

       Examples:

       default_database_type = hash
       default_database_type = dbm

default_delivery_slot_cost (default: 5)
       How often the Postfix queue manager's scheduler is allowed  to  preempt
       delivery of one message with another.

       Each  transport maintains a so-called "available delivery slot counter"
       for each message. One message can be preempted by another one when  the
       other  message  can  be  delivered  using no more delivery slots (i.e.,
       invocations of delivery agents) than the current  message  counter  has
       accumulated  (or  will  eventually  accumulate  -  see about slot loans
       below). This parameter controls how often is the counter incremented  -
       it  happens  after each default_delivery_slot_cost recipients have been
       delivered.

       The cost of 0 is used to disable the preempting scheduling  completely.
       The minimum value the scheduling algorithm can use is 2 - use it if you
       want to maximize the message throughput rate. Although there is no max-
       imum, it doesn't make much sense to use values above say 50.

       The  only  reason why the value of 2 is not the default is the way this
       parameter affects the delivery of mailing-list mail. In the worst case,
       their   delivery   can   take   somewhere   between  (cost+1/cost)  and
       (cost/cost-1) times more than if the preemptive scheduler was disabled.
       The default value of 5 turns out to provide reasonable message response
       times while making sure the mailing-list deliveries are not extended by
       more than 20-25 percent even in the worst case.

       Use  transport_delivery_slot_cost to specify a transport-specific over-
       ride, where transport is the master.cf name  of  the  message  delivery
       transport.

       Examples:

       default_delivery_slot_cost = 0
       default_delivery_slot_cost = 2

default_delivery_slot_discount (default: 50)
       The  default  value for transport-specific _delivery_slot_discount set-
       tings.

       This parameter speeds up the moment when a message preemption can  hap-
       pen.  Instead  of  waiting  until  the  full  amount  of delivery slots
       required is available, the preemption can happen when  transport_deliv-
       ery_slot_discount  percent of the required amount plus transport_deliv-
       ery_slot_loan still remains to be  accumulated.   Note  that  the  full
       amount  will still have to be accumulated before another preemption can
       take place later.

       Use transport_delivery_slot_discount to  specify  a  transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_delivery_slot_loan (default: 3)
       The default value for transport-specific _delivery_slot_loan  settings.

       This  parameter speeds up the moment when a message preemption can hap-
       pen. Instead of  waiting  until  the  full  amount  of  delivery  slots
       required  is available, the preemption can happen when transport_deliv-
       ery_slot_discount percent of the required amount plus  transport_deliv-
       ery_slot_loan  still  remains  to  be  accumulated.  Note that the full
       amount will still have to be accumulated before another preemption  can
       take place later.

       Use  transport_delivery_slot_loan to specify a transport-specific over-
       ride, where transport is the master.cf name  of  the  message  delivery
       transport.

default_delivery_status_filter (default: empty)
       Optional filter to replace the delivery status code or explanatory text
       of successful or unsuccessful deliveries.   This  does  not  allow  the
       replacement  of  a  successful status code (2.X.X) with an unsuccessful
       status code (4.X.X or 5.X.X) or vice versa.

       The following parameters can be used to implement a filter for specific
       delivery   agents:   lmtp_delivery_status_filter,   local_delivery_sta-
       tus_filter, pipe_delivery_status_filter, smtp_delivery_status_filter or
       virtual_delivery_status_filter.  These parameters support the same fil-
       ter syntax as described here.

       Specify zero or more "type:table"  lookup  table  names,  separated  by
       comma  or whitespace. For each successful or unsuccessful delivery to a
       recipient, the tables are queried in the specified order with one  line
       of text that is structured as follows:

           enhanced-status-code SPACE explanatory-text

       The first table match wins. The lookup result must have the same struc-
       ture as the query, a successful status code (2.X.X)  must  be  replaced
       with  a  successful  status code, an unsuccessful status code (4.X.X or
       5.X.X) must be replaced with  an  unsuccessful  status  code,  and  the
       explanatory  text field must be non-empty. Other results will result in
       a warning.

       Example 1: convert specific soft TLS errors into hard errors, by  over-
       riding the first number in the enhanced status code.

           /etc/postfix/main.cf:
               smtp_delivery_status_filter = pcre:/etc/postfix/smtp_dsn_filter

           /etc/postfix/smtp_dsn_filter:
               /^4(\.\d+\.\d+ TLS is required, but host \S+ refused to start TLS: .+)/
                   5$1
               /^4(\.\d+\.\d+ TLS is required, but was not offered by host .+)/
                   5$1
               # Do not change the following into hard bounces. They may
               # result from a local configuration problem.
               # 4.\d+.\d+ TLS is required, but our TLS engine is unavailable
               # 4.\d+.\d+ TLS is required, but unavailable
               # 4.\d+.\d+ Cannot start TLS: handshake failure

       Example  2:  censor  the  per-recipient delivery status text so that it
       does not reveal the destination  command  or  filename  when  a  remote
       sender requests confirmation of successful delivery.

           /etc/postfix/main.cf:
               local_delivery_status_filter = pcre:/etc/postfix/local_dsn_filter

           /etc/postfix/local_dsn_filter:
               /^(2\S+ delivered to file).+/    $1
               /^(2\S+ delivered to command).+/ $1

       Notes:

             This feature will NOT override the soft_bounce safety net.

             This  feature will change the enhanced status code and text that
              is logged to the maillog file,  and  that  is  reported  to  the
              sender in delivery confirmation or non-delivery notifications.

       This feature is available in Postfix 3.0 and later.

default_destination_concurrency_failed_cohort_limit (default: 1)
       How  many  pseudo-cohorts  must  suffer connection or handshake failure
       before a specific destination is considered  unavailable  (and  further
       delivery  is suspended). Specify zero to disable this feature. A desti-
       nation's pseudo-cohort failure count is reset each time a delivery com-
       pletes without connection or handshake failure for that specific desti-
       nation.

       A pseudo-cohort is the number of deliveries equal  to  a  destination's
       delivery concurrency.

       Use  transport_destination_concurrency_failed_cohort_limit to specify a
       transport-specific override, where transport is the master.cf  name  of
       the message delivery transport.

       This  feature  is available in Postfix 2.5. The default setting is com-
       patible with earlier Postfix versions.

default_destination_concurrency_limit (default: 20)
       The default maximal number of parallel deliveries to the same  destina-
       tion.  This is the default limit for delivery via the lmtp(8), pipe(8),
       smtp(8) and virtual(8) delivery agents.  With per-destination recipient
       limit > 1, a destination is a domain, otherwise it is a recipient.

       Use transport_destination_concurrency_limit to specify a transport-spe-
       cific override, where transport is the master.cf name  of  the  message
       delivery transport.

default_destination_concurrency_negative_feedback (default: 1)
       The  per-destination  amount of delivery concurrency negative feedback,
       after a delivery completes with  a  connection  or  handshake  failure.
       Feedback  values  are  in the range 0..1 inclusive. With negative feed-
       back, concurrency is decremented at the  beginning  of  a  sequence  of
       length  1/feedback. This is unlike positive feedback, where concurrency
       is incremented at the end of a sequence of length 1/feedback.

       As of Postfix version 2.5, negative  feedback  cannot  reduce  delivery
       concurrency  to  zero.   Instead, a destination is marked dead (further
       delivery  suspended)  after  the  failed  pseudo-cohort  count  reaches
       $default_destination_concurrency_failed_cohort_limit     (or    $trans-
       port_destination_concurrency_failed_cohort_limit).  To make the  sched-
       uler  completely  immune to connection or handshake failures, specify a
       zero feedback value and a zero failed pseudo-cohort limit.

       Specify one of the following forms:

       number

       number / number
              Constant feedback. The value must be in the  range  0..1  inclu-
              sive.   The  default  setting  of "1" is compatible with Postfix
              versions before 2.5, where a destination's delivery  concurrency
              is throttled down to zero (and further delivery suspended) after
              a single failed pseudo-cohort.

       number / concurrency
              Variable feedback of "number  /  (delivery  concurrency)".   The
              number must be in the range 0..1 inclusive. With number equal to
              "1", a destination's delivery concurrency is  decremented  by  1
              after each failed pseudo-cohort.

       A  pseudo-cohort  is  the number of deliveries equal to a destination's
       delivery concurrency.

       Use transport_destination_concurrency_negative_feedback  to  specify  a
       transport-specific  override,  where transport is the master.cf name of
       the message delivery transport.

       This feature is available in Postfix 2.5. The default setting  is  com-
       patible with earlier Postfix versions.

default_destination_concurrency_positive_feedback (default: 1)
       The  per-destination  amount of delivery concurrency positive feedback,
       after a delivery completes without  connection  or  handshake  failure.
       Feedback  values  are  in  the  range  0..1 inclusive.  The concurrency
       increases until it  reaches  the  per-destination  maximal  concurrency
       limit. With positive feedback, concurrency is incremented at the end of
       a sequence with length 1/feedback. This is  unlike  negative  feedback,
       where  concurrency  is decremented at the start of a sequence of length
       1/feedback.

       Specify one of the following forms:

       number

       number / number
              Constant feedback.  The value must be in the range  0..1  inclu-
              sive. The default setting of "1" is compatible with Postfix ver-
              sions before 2.5, where  a  destination's  delivery  concurrency
              doubles after each successful pseudo-cohort.

       number / concurrency
              Variable  feedback  of  "number  / (delivery concurrency)".  The
              number must be in the range 0..1 inclusive. With number equal to
              "1",  a  destination's  delivery concurrency is incremented by 1
              after each successful pseudo-cohort.

       A pseudo-cohort is the number of deliveries equal  to  a  destination's
       delivery concurrency.

       Use  transport_destination_concurrency_positive_feedback  to  specify a
       transport-specific override, where transport is the master.cf  name  of
       the message delivery transport.

       This feature is available in Postfix 2.5 and later.

default_destination_rate_delay (default: 0s)
       The  default amount of delay that is inserted between individual deliv-
       eries to the same destination; the resulting behavior  depends  on  the
       value of the corresponding per-destination recipient limit.

             With  a  corresponding  per-destination recipient limit > 1, the
              rate delay specifies the time between  deliveries  to  the  same
              domain.  Different domains are delivered in parallel, subject to
              the process limits specified in master.cf.

             With a corresponding per-destination recipient limit equal to 1,
              the rate delay specifies the time between deliveries to the same
              recipient. Different recipients are delivered in parallel,  sub-
              ject to the process limits specified in master.cf.

       To  enable  the delay, specify a non-zero time value (an integral value
       plus an optional one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       NOTE: the delay is enforced by the queue manager. The delay timer state
       does not survive "postfix reload" or "postfix stop".

       Use transport_destination_rate_delay to  specify  a  transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       NOTE: with a non-zero _destination_rate_delay, specify a transport_des-
       tination_concurrency_failed_cohort_limit of 10 or more to prevent Post-
       fix from deferring all mail for the same  destination  after  only  one
       connection or handshake error.

       This feature is available in Postfix 2.5 and later.

default_destination_recipient_limit (default: 50)
       The default maximal number of recipients per message delivery.  This is
       the default limit for delivery via the lmtp(8),  pipe(8),  smtp(8)  and
       virtual(8) delivery agents.

       Setting this parameter to a value of 1 affects email deliveries as fol-
       lows:

             It changes the meaning of the corresponding per-destination con-
              currency  limit,  from  concurrency  of  deliveries  to the same
              domain into concurrency of deliveries  to  the  same  recipient.
              Different  recipients  are delivered in parallel, subject to the
              process limits specified in master.cf.

             It changes the meaning of the corresponding per-destination rate
              delay, from the delay between deliveries to the same domain into
              the delay between deliveries to the same recipient.  Again, dif-
              ferent  recipients  are  delivered  in  parallel, subject to the
              process limits specified in master.cf.

             It changes the meaning of  other  corresponding  per-destination
              settings  in a similar manner, from settings for delivery to the
              same domain into settings for delivery to the same recipient.

       Use transport_destination_recipient_limit to specify  a  transport-spe-
       cific  override,  where  transport is the master.cf name of the message
       delivery transport.

default_extra_recipient_limit (default: 1000)
       The default value for the extra per-transport limit imposed on the num-
       ber  of  in-memory  recipients.  This extra recipient space is reserved
       for the cases when the Postfix queue manager's scheduler  preempts  one
       message with another and suddenly needs some extra recipients slots for
       the chosen message in order to avoid performance degradation.

       Use transport_extra_recipient_limit  to  specify  a  transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_filter_nexthop (default: empty)
       When a content_filter or FILTER request specifies no explicit  next-hop
       destination,  use  $default_filter_nexthop  instead; when that value is
       empty, use the domain in the recipient address.  Specify  "default_fil-
       ter_nexthop  =  $myhostname" for compatibility with Postfix version 2.6
       and earlier, or specify an explicit next-hop destination with each con-
       tent_filter value or FILTER action.

       This feature is available in Postfix 2.7 and later.

default_minimum_delivery_slots (default: 3)
       How  many recipients a message must have in order to invoke the Postfix
       queue manager's scheduling algorithm  at  all.   Messages  which  would
       never  accumulate  at  least  this many delivery slots (subject to slot
       cost parameter as well) are never preempted.

       Use transport_minimum_delivery_slots to  specify  a  transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

default_privs (default: nobody)
       The default rights used by the local(8) delivery agent for delivery  to
       external  file  or  command.   These  rights  are used when delivery is
       requested from an aliases(5) file that is owned by root, or when deliv-
       ery  is done on behalf of root. DO NOT SPECIFY A PRIVILEGED USER OR THE
       POSTFIX OWNER.

default_process_limit (default: 100)
       The default maximal number of Postfix child processes  that  provide  a
       given service. This limit can be overruled for specific services in the
       master.cf file.

default_rbl_reply (default: see postconf -d output)
       The default Postfix SMTP server response template for a request that is
       rejected by an RBL-based restriction. This template can be overruled by
       specific entries in the optional rbl_reply_maps lookup table.

       This feature is available in Postfix 2.0 and later.

       The template is subject to exactly one level of $name substitution:

       $client
              The client hostname and IP address, formatted as  name[address].

       $client_address
              The client IP address.

       $client_name
              The       client       hostname      or      "unknown".      See
              reject_unknown_client_hostname for more details.

       $reverse_client_name
              The client hostname from  address->name  lookup,  or  "unknown".
              See reject_unknown_reverse_client_hostname for more details.

       $helo_name
              The hostname given in HELO or EHLO command or empty string.

       $rbl_class
              The  blacklisted  entity type: Client host, Helo command, Sender
              address, or Recipient address.

       $rbl_code
              The  numerical  SMTP  response  code,  as  specified  with   the
              maps_rbl_reject_code  configuration parameter. Note: The numeri-
              cal SMTP response code is required, and must appear at the start
              of  the  reply. With Postfix version 2.3 and later this informa-
              tion may be followed by an RFC 3463 enhanced status code.

       $rbl_domain
              The RBL domain where $rbl_what is blacklisted.

       $rbl_reason
              The reason why $rbl_what is blacklisted, or an empty string.

       $rbl_what
              The entity that is blacklisted (an IP  address,  a  hostname,  a
              domain  name, or an email address whose domain was blacklisted).

       $recipient
              The recipient address or <> in case of the null address.

       $recipient_domain
              The recipient domain or empty string.

       $recipient_name
              The recipient address localpart or <> in case of null address.

       $sender
              The sender address or <> in case of the null address.

       $sender_domain
              The sender domain or empty string.

       $sender_name
              The sender address localpart or <> in case of the null  address.

       ${name?text}
              Expands to `text' if $name is not empty.

       ${name:text}
              Expands to `text' if $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Note:  when  an  enhanced status code is specified in an RBL reply tem-
       plate, it is subject to modification.   The  following  transformations
       are  needed  when the same RBL reply template is used for client, helo,
       sender, or recipient access restrictions.

             When rejecting a sender address, the Postfix  SMTP  server  will
              transform  a  recipient  DSN status (e.g., 4.1.1-4.1.6) into the
              corresponding sender DSN status, and vice versa.

             When rejecting non-address information (such as the HELO command
              argument  or  the  client  hostname/address),  the  Postfix SMTP
              server will transform a sender or recipient DSN  status  into  a
              generic non-address DSN status (e.g., 4.0.0).

default_recipient_limit (default: 20000)
       The default per-transport upper limit on the number of in-memory recip-
       ients.  These limits take priority over the global qmgr_message_recipi-
       ent_limit  after the message has been assigned to the respective trans-
       ports.  See also default_extra_recipient_limit and qmgr_message_recipi-
       ent_minimum.

       Use transport_recipient_limit to specify a transport-specific override,
       where transport is the master.cf name of the  message  delivery  trans-
       port.

default_recipient_refill_delay (default: 5s)
       The  default  per-transport  maximum  delay between recipients refills.
       When not all message recipients fit into the memory at once, keep load-
       ing  more  of them at least once every this many seconds.  This is used
       to make sure the recipients are refilled in  timely  manner  even  when
       $default_recipient_refill_limit is too high for too slow deliveries.

       Use  transport_recipient_refill_delay  to  specify a transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       This feature is available in Postfix 2.4 and later.

default_recipient_refill_limit (default: 100)
       The default per-transport limit on the number of recipients refilled at
       once.  When not all message recipients fit into  the  memory  at  once,
       keep  loading  more of them in batches of at least this many at a time.
       See also $default_recipient_refill_delay, which may result in recipient
       batches lower than this when this limit is too high for too slow deliv-
       eries.

       Use transport_recipient_refill_limit to  specify  a  transport-specific
       override, where transport is the master.cf name of the message delivery
       transport.

       This feature is available in Postfix 2.4 and later.

default_transport (default: smtp)
       The default mail delivery transport and next-hop destination for desti-
       nations   that   do   not   match   $mydestination,   $inet_interfaces,
       $proxy_interfaces, $virtual_alias_domains, $virtual_mailbox_domains, or
       $relay_domains.    This   information   can   be   overruled  with  the
       sender_dependent_default_transport_maps parameter and with  the  trans-
       port(5) table.

       In  order  of  decreasing  precedence, the nexthop destination is taken
       from   $sender_dependent_default_transport_maps,    $default_transport,
       $sender_dependent_relayhost_maps,  $relayhost,  or  from  the recipient
       domain.

       Specify a string of the form transport:nexthop, where transport is  the
       name  of  a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       Example:

       default_transport = uucp:relayhostname

default_transport_rate_delay (default: 0s)
       The  default amount of delay that is inserted between individual deliv-
       eries over the same message delivery transport, regardless of  destina-
       tion. If non-zero, all deliveries over the same message delivery trans-
       port will happen one at a time.

       Use  transport_transport_rate_delay  to  specify  a  transport-specific
       override, where the initial transport is the master.cf name of the mes-
       sage delivery transport.

       Example: throttle outbound SMTP  mail  to  at  most  3  deliveries  per
       minute.

       /etc/postfix/main.cf:
           smtp_transport_rate_delay = 20s

       To  enable  the delay, specify a non-zero time value (an integral value
       plus an optional one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       NOTE: the delay is enforced by the queue manager.

       This feature is available in Postfix 3.1 and later.

default_verp_delimiters (default: +=)
       The  two  default  VERP  delimiter  characters.  These are used when no
       explicit delimiters are specified with the SMTP XVERP command  or  with
       the  "sendmail  -V"  command-line  option.  Specify characters that are
       allowed by the verp_delimiter_filter setting.

       This feature is available in Postfix 1.1 and later.

defer_code (default: 450)
       The numerical Postfix SMTP server response  code  when  a  remote  SMTP
       client request is rejected by the "defer" restriction.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

defer_service_name (default: defer)
       The name of the defer service.  This  service  is  implemented  by  the
       bounce(8) daemon and maintains a record of failed delivery attempts and
       generates non-delivery notifications.

       This feature is available in Postfix 2.0 and later.

defer_transports (default: empty)
       The names of message delivery transports that should not  deliver  mail
       unless someone issues "sendmail -q" or equivalent. Specify zero or more
       names of mail delivery transports names that appear in the first  field
       of master.cf.

       Example:

       defer_transports = smtp

delay_logging_resolution_limit (default: 2)
       The  maximal  number  of  digits  after  the decimal point when logging
       sub-second delay values.  Specify a number in the range 0..6.

       Large delay values are rounded off to an integral number seconds; delay
       values  below the delay_logging_resolution_limit are logged as "0", and
       delay values under 100s are logged with at most two-digit precision.

       The format of the "delays=a/b/c/d" logging is as follows:

             a = time from message arrival to last active queue entry

             b = time from last active queue entry to connection setup

             c = time in connection setup, including DNS, EHLO and STARTTLS

             d = time in message transmission

       This feature is available in Postfix 2.3 and later.

delay_notice_recipient (default: postmaster)
       The recipient of postmaster notifications with the message  headers  of
       mail that cannot be delivered within $delay_warning_time time units.

       See also: delay_warning_time, notify_classes.

delay_warning_time (default: 0h)
       The  time after which the sender receives a copy of the message headers
       of mail that is still queued. The confirm_delay_cleared parameter  con-
       trols sender notification when the delay clears up.

       To  enable  this  feature,  specify  a non-zero time value (an integral
       value plus an optional one-letter suffix that specifies the time unit).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is h (hours).

       See     also:     delay_notice_recipient,     notify_classes,      con-
       firm_delay_cleared.

deliver_lock_attempts (default: 20)
       The  maximal number of attempts to acquire an exclusive lock on a mail-
       box file or bounce(8) logfile.

deliver_lock_delay (default: 1s)
       The time between attempts to acquire an exclusive  lock  on  a  mailbox
       file or bounce(8) logfile.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

destination_concurrency_feedback_debug (default: no)
       Make the queue manager's feedback  algorithm  verbose  for  performance
       analysis purposes.

       This feature is available in Postfix 2.5 and later.

detect_8bit_encoding_header (default: yes)
       Automatically detect 8BITMIME body content by looking at Content-Trans-
       fer-Encoding:  message  headers;  historically,   this   behavior   was
       hard-coded to be "always on".

       This feature is available in Postfix 2.5 and later.

disable_dns_lookups (default: no)
       Disable  DNS  lookups  in  the Postfix SMTP and LMTP clients. When dis-
       abled, hosts are looked up with the getaddrinfo() system  library  rou-
       tine which normally also looks in /etc/hosts.  As of Postfix 2.11, this
       parameter is deprecated; use smtp_dns_support_level instead.

       DNS lookups are enabled by default.

disable_mime_input_processing (default: no)
       Turn off MIME processing while receiving mail. This means that no  spe-
       cial  treatment is given to Content-Type: message headers, and that all
       text after the initial message headers is considered to be part of  the
       message body.

       This feature is available in Postfix 2.0 and later.

       Mime  input processing is enabled by default, and is needed in order to
       recognize MIME headers in message content.

disable_mime_output_conversion (default: no)
       Disable the conversion of 8BITMIME format to 7BIT format.  Mime  output
       conversion  is  needed when the destination does not advertise 8BITMIME
       support.

       This feature is available in Postfix 2.0 and later.

disable_verp_bounces (default: no)
       Disable sending one bounce report per recipient.

       The default, one per recipient, is what ezmlm needs.

       This feature is available in Postfix 1.1 and later.

disable_vrfy_command (default: no)
       Disable the SMTP VRFY command. This stops some techniques used to  har-
       vest email addresses.

       Example:

       disable_vrfy_command = no

dns_ncache_ttl_fix_enable (default: no)
       Enable a workaround for future libc incompatibility. The Postfix imple-
       mentation of RFC 2308 negative reply caching relies on the promise that
       res_query()  and  res_search()  invoke  res_send(),  which  returns the
       server response in an application buffer even if the  requested  record
       does  not  exist.  If this promise is broken, specify "yes" to enable a
       workaround for DNS reputation lookups.

       This feature is available in Postfix 3.1 and later.

dnsblog_reply_delay (default: 0s)
       A debugging aid to artificially delay DNS responses.

       This feature is available in Postfix 2.8.

dnsblog_service_name (default: dnsblog)
       The name of the dnsblog(8) service entry  in  master.cf.  This  service
       performs DNS white/blacklist lookups.

       This feature is available in Postfix 2.8 and later.

dont_remove (default: 0)
       Don't remove queue files and save them to the "saved" mail queue.  This
       is a debugging aid.  To inspect the envelope information and content of
       a Postfix queue file, use the postcat(1) command.

double_bounce_sender (default: double-bounce)
       The  sender  address  of postmaster notifications that are generated by
       the mail system. All mail to this address  is  silently  discarded,  in
       order to terminate mail bounce loops.

duplicate_filter_limit (default: 1000)
       The  maximal  number  of  addresses remembered by the address duplicate
       filter for aliases(5) or virtual(5) alias expansion,  or  for  showq(8)
       queue displays.

empty_address_default_transport_maps_lookup_key (default: <>)
       The  sender_dependent_default_transport_maps search string that will be
       used instead of the null sender address.

       This feature is available in Postfix 2.7 and later.

empty_address_recipient (default: MAILER-DAEMON)
       The recipient of mail addressed to the null address.  Postfix does  not
       accept  such  addresses in SMTP commands, but they may still be created
       locally as the result of configuration or software error.

empty_address_relayhost_maps_lookup_key (default: <>)
       The sender_dependent_relayhost_maps search string  that  will  be  used
       instead of the null sender address.

       This  feature  is available in Postfix 2.5 and later. With earlier ver-
       sions, sender_dependent_relayhost_maps lookups  were  skipped  for  the
       null sender address.

enable_errors_to (default: no)
       Report mail delivery errors to the address specified with the non-stan-
       dard Errors-To: message header, instead of the envelope sender  address
       (this  feature  is  removed  with Postfix version 2.2, is turned off by
       default with Postfix version 2.1, and is always turned  on  with  older
       Postfix versions).

enable_long_queue_ids (default: no)
       Enable  long, non-repeating, queue IDs (queue file names).  The benefit
       of non-repeating names is simpler logfile  analysis  and  easier  queue
       migration  (there  is  no  need to run "postsuper" to change queue file
       names that don't match their message file inode number).

       Note: see below for how to convert long queue file names to Postfix  <=
       2.8.

       Changing the parameter value to "yes" has the following effects:

             Existing queue file names are not affected.

             New  queue files are created with names such as 3Pt2mN2VXxznjll.
              These are encoded in a 52-character alphabet that contains  dig-
              its  (0-9),  upper-case  letters  (B-Z)  and  lower-case letters
              (b-z). For safety reasons the vowels (AEIOUaeiou)  are  excluded
              from the alphabet.  The name format is: 6 or more characters for
              the time in seconds, 4 characters for the time in  microseconds,
              the  'z';  the remainder is the file inode number encoded in the
              first 51 characters of the 52-character alphabet.

             New messages have a Message-ID header with queueID@myhostname.

             The mailq (postqueue -p) output has a  wider  Queue  ID  column.
              The number of whitespace-separated fields is not changed.

             The  hash_queue_depth algorithm uses the first characters of the
              queue file creation time in microseconds, after conversion  into
              hexadecimal representation. This produces the same queue hashing
              behavior  as  if  the  queue  file   name   was   created   with
              "enable_long_queue_ids = no".

       Changing the parameter value to "no" has the following effects:

             Existing  long  queue  file  names are renamed to the short form
              (while running "postfix reload" or "postsuper").

             New queue files are created with names such as C3CD21F3E90  from
              a hexadecimal alphabet that contains digits (0-9) and upper-case
              letters (A-F). The name format is: 5 characters for the time  in
              microseconds; the remainder is the file inode number.

             New   messages   have   a  Message-ID  header  with  YYYYMMDDHH-
              MMSS.queueid@myhostname,  where  YYYYMMDDHHMMSS  are  the  year,
              month, day, hour, minute and second.

             The  mailq  (postqueue  -p)  output  has the same format as with
              Postfix <= 2.8.

             The hash_queue_depth algorithm uses the first characters of  the
              queue file name, with the hexadecimal representation of the file
              creation time in microseconds.

       Before migration to Postfix <= 2.8, the following commands are required
       to convert long queue file names into short names:

       # postfix stop
       # postconf enable_long_queue_ids=no
       # postsuper

       Repeat  the  postsuper command until it reports no more queue file name
       changes.

       This feature is available in Postfix 2.9 and later.

enable_original_recipient (default: yes)
       Enable support for the X-Original-To message  header.  This  header  is
       needed for multi-recipient mailboxes.

       When  this  parameter  is  set  to  yes, the cleanup(8) daemon performs
       duplicate elimination on distinct pairs of (original recipient, rewrit-
       ten  recipient),  and generates non-empty original recipient queue file
       records.

       When this parameter is set to no, the cleanup(8) daemon performs dupli-
       cate elimination on the rewritten recipient address only, and generates
       empty original recipient queue file records.

       This feature is available in Postfix 2.1 and later. With  Postfix  ver-
       sion 2.0, support for the X-Original-To message header is always turned
       on. Postfix versions before 2.0 have no support for  the  X-Original-To
       message header.

error_notice_recipient (default: postmaster)
       The  recipient of postmaster notifications about mail delivery problems
       that are caused by  policy,  resource,  software  or  protocol  errors.
       These notifications are enabled with the notify_classes parameter.

error_service_name (default: error)
       The  name  of  the  error(8) pseudo delivery agent. This service always
       returns mail as undeliverable.

       This feature is available in Postfix 2.0 and later.

execution_directory_expansion_filter (default: see postconf -d output)
       Restrict the characters that the  local(8)  delivery  agent  allows  in
       $name  expansions  of $command_execution_directory.  Characters outside
       the allowed set are replaced by underscores.

       This feature is available in Postfix 2.2 and later.

expand_owner_alias (default: no)
       When delivering to an alias "aliasname" that has  an  "owner-aliasname"
       companion  alias,  set  the envelope sender address to the expansion of
       the "owner-aliasname" alias. Normally, Postfix sets the envelope sender
       address to the name of the "owner-aliasname" alias.

export_environment (default: see postconf -d output)
       The list of environment variables that a Postfix process will export to
       non-Postfix processes. The TZ variable is needed for sane time  keeping
       on System-V-ish systems.

       Specify  a  list  of names and/or name=value pairs, separated by white-
       space or comma. Specify "{ name=value }" to protect whitespace or comma
       in  parameter  values (whitespace after "{" and before "}" is ignored).
       The form name=value is supported with Postfix version  2.1  and  later;
       the use of {} is supported with Postfix 3.0 and later.

       Example:

       export_environment = TZ PATH=/bin:/usr/bin

extract_recipient_limit (default: 10240)
       The  maximal  number  of  recipient addresses that Postfix will extract
       from message headers when mail is submitted with "sendmail -t".

       This feature was removed in Postfix version 2.1.

fallback_relay (default: empty)
       Optional list of relay hosts for SMTP destinations that can't be  found
       or  that are unreachable. With Postfix 2.3 this parameter is renamed to
       smtp_fallback_relay.

       By default, mail is returned to the sender when a  destination  is  not
       found, and delivery is deferred when a destination is unreachable.

       The  fallback relays must be SMTP destinations. Specify a domain, host,
       host:port, [host]:port, [address] or [address]:port;  the  form  [host]
       turns off MX lookups.  If you specify multiple SMTP destinations, Post-
       fix will try them in the specified order.

       Note: before Postfix 2.2, do not use the  fallback_relay  feature  when
       relaying  mail  for  a  backup  or  primary  MX domain. Mail would loop
       between the Postfix MX host and the fallback_relay host when the  final
       destination is unavailable.

             In main.cf specify "relay_transport = relay",

             In  master.cf specify "-o fallback_relay =" (i.e., empty) at the
              end of the relay entry.

             In transport maps, specify "relay:nexthop..."  as the right-hand
              side for backup or primary MX domain entries.

       Postfix  version  2.2 and later will not use the fallback_relay feature
       for destinations that it is MX host for.

fallback_transport (default: empty)
       Optional message delivery transport that the  local(8)  delivery  agent
       should use for names that are not found in the aliases(5) or UNIX pass-
       word database.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

fallback_transport_maps (default: empty)
       Optional  lookup  tables with per-recipient message delivery transports
       for recipients that the local(8) delivery agent could not find  in  the
       aliases(5) or UNIX password database.

       The  precedence  of  local(8)  delivery  features  from high to low is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps,  mailbox_command, home_mailbox, mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       For safety reasons, this feature does not allow  $number  substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

fast_flush_domains (default: $relay_domains)
       Optional  list  of  destinations  that are eligible for per-destination
       logfiles with mail that is queued to those destinations.

       By default, Postfix maintains "fast flush" logfiles only  for  destina-
       tions  that  the  Postfix  SMTP server is willing to relay to (i.e. the
       default   is:   "fast_flush_domains   =   $relay_domains";   see    the
       relay_domains parameter in the postconf(5) manual).

       Specify  a list of hosts or domains, "/file/name" patterns or "type:ta-
       ble" lookup tables, separated by commas  and/or  whitespace.   Continue
       long  lines  by  starting the next line with whitespace. A "/file/name"
       pattern is replaced by its contents; a  "type:table"  lookup  table  is
       matched when the domain or its parent domain appears as lookup key.

       Pattern  matching  of  domain  names  is  controlled by the presence or
       absence of "fast_flush_domains" in the parent_domain_matches_subdomains
       parameter value.

       Specify  "fast_flush_domains  ="  (i.e.,  empty) to disable the feature
       altogether.

fast_flush_purge_time (default: 7d)
       The time after which an empty per-destination "fast flush"  logfile  is
       deleted.

       You can specify the time as a number, or as a number followed by a let-
       ter that  indicates  the  time  unit:  s=seconds,  m=minutes,  h=hours,
       d=days, w=weeks.  The default time unit is days.

fast_flush_refresh_time (default: 12h)
       The  time  after  which  a  non-empty  but unread per-destination "fast
       flush" logfile needs to be refreshed.  The contents of  a  logfile  are
       refreshed by requesting delivery of all messages listed in the logfile.

       You can specify the time as a number, or as a number followed by a let-
       ter  that  indicates  the  time  unit:  s=seconds,  m=minutes, h=hours,
       d=days, w=weeks.  The default time unit is hours.

fault_injection_code (default: 0)
       Force specific internal tests to fail, to test the handling  of  errors
       that are difficult to reproduce otherwise.

flush_service_name (default: flush)
       The  name  of the flush(8) service. This service maintains per-destina-
       tion logfiles with the queue file names of  mail  that  is  queued  for
       those destinations.

       This feature is available in Postfix 2.0 and later.

fork_attempts (default: 5)
       The maximal number of attempts to fork() a child process.

fork_delay (default: 1s)
       The delay between attempts to fork() a child process.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

forward_expansion_filter (default: see postconf -d output)
       Restrict the characters that the  local(8)  delivery  agent  allows  in
       $name  expansions of $forward_path.  Characters outside the allowed set
       are replaced by underscores.

forward_path (default: see postconf -d output)
       The local(8) delivery agent search list for  finding  a  .forward  file
       with  user-specified  delivery methods. The first file that is found is
       used.

       The following $name expansions are  done  on  forward_path  before  the
       search actually happens. The result of $name expansion is filtered with
       the character set that is specified with  the  forward_expansion_filter
       parameter.

       $user  The recipient's username.

       $shell The recipient's login shell pathname.

       $home  The recipient's home directory.

       $recipient
              The full recipient address.

       $extension
              The optional recipient address extension.

       $domain
              The recipient domain.

       $local The entire recipient localpart.

       $recipient_delimiter
              The  address extension delimiter that was found in the recipient
              address (Postfix 2.11 and later), or the  system-wide  recipient
              address extension delimiter (Postfix 2.10 and earlier).

       ${name?value}
              Expands to value when $name is non-empty.

       ${name:value}
              Expands to value when $name is empty.

       Instead of $name you can also specify ${name} or $(name).

       Examples:

       forward_path = /var/forward/$user
       forward_path =
           /var/forward/$user/.forward$recipient_delimiter$extension,
           /var/forward/$user/.forward

frozen_delivered_to (default: yes)
       Update  the local(8) delivery agent's idea of the Delivered-To: address
       (see prepend_delivered_header) only once, at the start  of  a  delivery
       attempt;  do  not  update  the  Delivered-To:  address  while expanding
       aliases or .forward files.

       This feature is available in Postfix 2.3 and later. With older  Postfix
       releases,  the behavior is as if this parameter is set to "no". The old
       setting can be expensive with deeply nested aliases or .forward  files.
       When  an  alias  or .forward file changes the Delivered-To: address, it
       ties up one queue file and one cleanup process instance while  mail  is
       being forwarded.

hash_queue_depth (default: 1)
       The number of subdirectory levels for queue directories listed with the
       hash_queue_names parameter. Queue hashing is  implemented  by  creating
       one  or  more  levels  of directories with one-character names.  Origi-
       nally, these directory names were equal to the first characters of  the
       queue  file  name, with the hexadecimal representation of the file cre-
       ation time in microseconds.

       With long queue file names, queue hashing produces the same results  as
       with  short  names. The file creation time in microseconds is converted
       into hexadecimal form before the result is used for queue hashing.  The
       base  16 encoding gives finer control over the number of subdirectories
       than is possible with the base 52 encoding of long queue file names.

       After changing the hash_queue_names or hash_queue_depth parameter, exe-
       cute the command "postfix reload".

hash_queue_names (default: deferred, defer)
       The names of queue directories that are split across multiple subdirec-
       tory levels.

       Before Postfix version 2.2, the default list of hashed queues was  sig-
       nificantly  larger. Claims about improvements in file system technology
       suggest that hashing of the incoming and active  queues  is  no  longer
       needed.  Fewer  hashed  directories speed up the time needed to restart
       Postfix.

       After changing the hash_queue_names or hash_queue_depth parameter, exe-
       cute the command "postfix reload".

header_address_token_limit (default: 10240)
       The  maximal number of address tokens are allowed in an address message
       header. Information that exceeds the limit is discarded.  The limit  is
       enforced by the cleanup(8) server.

header_checks (default: empty)
       Optional  lookup tables for content inspection of primary non-MIME mes-
       sage headers, as specified in the header_checks(5) manual page.

header_size_limit (default: 102400)
       The maximal amount of memory in bytes for storing a message header.  If
       a  header is larger, the excess is discarded.  The limit is enforced by
       the cleanup(8) server.

helpful_warnings (default: yes)
       Log warnings about  problematic  configuration  settings,  and  provide
       helpful suggestions.

       This feature is available in Postfix 2.0 and later.

home_mailbox (default: empty)
       Optional  pathname of a mailbox file relative to a local(8) user's home
       directory.

       Specify a pathname ending in "/" for qmail-style delivery.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       Examples:

       home_mailbox = Mailbox
       home_mailbox = Maildir/

hopcount_limit (default: 50)
       The maximal number of Received:  message headers that is allowed in the
       primary message headers. A message that exceeds the limit  is  bounced,
       in order to stop a mailer loop.

html_directory (default: see postconf -d output)
       The  location of Postfix HTML files that describe how to build, config-
       ure or operate a specific Postfix subsystem or feature.

ignore_mx_lookup_error (default: no)
       Ignore DNS MX lookups that produce no response.  By default, the  Post-
       fix SMTP client defers delivery and tries again after some delay.  This
       behavior is required by the SMTP standard.

       Specify "ignore_mx_lookup_error = yes" to force a DNS A  record  lookup
       instead. This violates the SMTP standard and can result in mis-delivery
       of mail.

import_environment (default: see postconf -d output)
       The list of environment parameters that a Postfix process  will  import
       from a non-Postfix parent process. Examples of relevant parameters:

       TZ     Needed for sane time keeping on most System-V-ish systems.

       DISPLAY
              Needed for debugging Postfix daemons with an X-windows debugger.

       XAUTHORITY
              Needed for debugging Postfix daemons with an X-windows debugger.

       MAIL_CONFIG
              Needed to make "postfix -c" work.

       Specify  a  list  of names and/or name=value pairs, separated by white-
       space or comma. Specify "{ name=value }" to protect whitespace or comma
       in  parameter  values (whitespace after "{" and before "}" is ignored).
       The form name=value is supported with Postfix version  2.1  and  later;
       the use of {} is supported with Postfix 3.0 and later.

in_flow_delay (default: 1s)
       Time  to pause before accepting a new message, when the message arrival
       rate exceeds the message delivery rate. This feature is  turned  on  by
       default (it's disabled on SCO UNIX due to an SCO bug).

       With  the default 100 Postfix SMTP server process limit, "in_flow_delay
       = 1s" limits the mail inflow to 100 messages per second above the  num-
       ber of messages delivered per second.

       Specify 0 to disable the feature. Valid delays are 0..10.

inet_interfaces (default: all)
       The network interface addresses that this mail system receives mail on.
       Specify "all" to receive mail on all network interfaces (default),  and
       "loopback-only"  to  receive  mail  on loopback network interfaces only
       (Postfix version 2.2 and later).  The parameter also controls  delivery
       of mail to user@[ip.address].

       Note 1: you need to stop and start Postfix when this parameter changes.

       Note 2: address information may be enclosed inside [], but this form is
       not required here.

       When  inet_interfaces  specifies just one IPv4 and/or IPv6 address that
       is not a loopback address,  the  Postfix  SMTP  client  will  use  this
       address as the IP source address for outbound mail. Support for IPv6 is
       available in Postfix version 2.2 and later.

       On a multi-homed firewall with separate Postfix instances listening  on
       the  "inside"  and "outside" interfaces, this can prevent each instance
       from being able to reach remote SMTP servers on the "other side" of the
       firewall.  Setting  smtp_bind_address  to  0.0.0.0 avoids the potential
       problem for IPv4, and setting smtp_bind_address6 to :: solves the prob-
       lem for IPv6.

       A better solution for multi-homed firewalls is to leave inet_interfaces
       at the default value and instead use explicit IP addresses in the  mas-
       ter.cf  SMTP  server  definitions.   This  preserves  the  Postfix SMTP
       client's loop detection, by ensuring that each  side  of  the  firewall
       knows  that  the  other  IP  address  is  still  the same host. Setting
       $inet_interfaces to a single IPv4 and/or IPV6 address is primarily use-
       ful  with  virtual  hosting  of domains on secondary IP addresses, when
       each IP address serves a different domain (and has a different $myhost-
       name setting).

       See also the proxy_interfaces parameter, for network addresses that are
       forwarded to Postfix by way of a proxy or address translator.

       Examples:

       inet_interfaces = all (DEFAULT)
       inet_interfaces = loopback-only (Postfix version 2.2 and later)
       inet_interfaces = 127.0.0.1
       inet_interfaces = 127.0.0.1, [::1] (Postfix version 2.2 and later)
       inet_interfaces = 192.168.1.2, 127.0.0.1

inet_protocols (default: all)
       The Internet protocols Postfix will  attempt  to  use  when  making  or
       accepting  connections.  Specify one or more of "ipv4" or "ipv6", sepa-
       rated by whitespace or commas. The form "all" is equivalent  to  "ipv4,
       ipv6"  or  "ipv4", depending on whether the operating system implements
       IPv6.

       With Postfix 2.8 and earlier the default is "ipv4". For backwards  com-
       patibility  with these releases, the Postfix 2.9 and later upgrade pro-
       cedure appends an explicit "inet_protocols = ipv4" setting  to  main.cf
       when no explicit setting is present. This compatibility workaround will
       be phased out as IPv6 deployment becomes more common.

       This feature is available in Postfix 2.2 and later.

       Note: you MUST stop and start Postfix after changing this parameter.

       On systems that pre-date IPV6_V6ONLY support (RFC 3493), an IPv6 server
       will  also  accept  IPv4 connections, even when IPv4 is turned off with
       the inet_protocols parameter.  On  systems  with  IPV6_V6ONLY  support,
       Postfix  will  use  separate server sockets for IPv6 and IPv4, and each
       will accept only connections for the corresponding protocol.

       When IPv4 support is enabled via the inet_protocols parameter,  Postfix
       will  look  up DNS type A records, and will convert IPv4-in-IPv6 client
       IP addresses (::ffff:1.2.3.4) to their original  IPv4  form  (1.2.3.4).
       The  latter  is  needed on hosts that pre-date IPV6_V6ONLY support (RFC
       3493).

       When IPv6 support is enabled via the inet_protocols parameter,  Postfix
       will do DNS type AAAA record lookups.

       When  both  IPv4  and IPv6 support are enabled, the Postfix SMTP client
       will choose the protocol as specified with the  smtp_address_preference
       parameter.  Postfix  versions  before  2.8  attempt to connect via IPv6
       before attempting to use IPv4.

       Examples:

       inet_protocols = ipv4
       inet_protocols = all (DEFAULT)
       inet_protocols = ipv6
       inet_protocols = ipv4, ipv6

initial_destination_concurrency (default: 5)
       The initial per-destination concurrency level for parallel delivery  to
       the same destination.  With per-destination recipient limit > 1, a des-
       tination is a domain, otherwise it is a recipient.

       Use  transport_initial_destination_concurrency  to  specify  a   trans-
       port-specific  override,  where  transport is the master.cf name of the
       message delivery transport (Postfix 2.5 and later).

       Warning: with concurrency of 1, one bad message can be enough to  block
       all mail to a site.

internal_mail_filter_classes (default: empty)
       What  categories  of Postfix-generated mail are subject to before-queue
       content inspection by non_smtpd_milters, header_checks and body_checks.
       Specify  zero  or  more  of  the  following, separated by whitespace or
       comma.

       bounce Inspect the content of delivery status notifications.

       notify Inspect the content of postmaster notifications by  the  smtp(8)
              and smtpd(8) processes.

       NOTE:  It's  generally  not  safe to enable content inspection of Post-
       fix-generated email messages. The user is warned.

       This feature is available in Postfix 2.3 and later.

invalid_hostname_reject_code (default: 501)
       The numerical Postfix SMTP server response code when the client HELO or
       EHLO  command parameter is rejected by the reject_invalid_helo_hostname
       restriction.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

ipc_idle (default: version dependent)
       The  time  after  which  a client closes an idle internal communication
       channel.  The purpose is to allow Postfix daemon processes to terminate
       voluntarily  after  they become idle. This is used, for example, by the
       Postfix address resolving and rewriting clients.

       With Postfix 2.4 the default value was reduced from 100s to 5s.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

ipc_timeout (default: 3600s)
       The  time  limit  for sending or receiving information over an internal
       communication channel.  The purpose is to break out of deadlock  situa-
       tions.  If  the time limit is exceeded the software aborts with a fatal
       error.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

ipc_ttl (default: 1000s)
       The  time  after which a client closes an active internal communication
       channel.  The purpose is to allow Postfix daemon processes to terminate
       voluntarily after reaching their client limit.  This is used, for exam-
       ple, by the Postfix address resolving and rewriting clients.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

line_length_limit (default: 2048)
       Upon  input,  long  lines  are  chopped  up into pieces of at most this
       length; upon delivery, long lines are reconstructed.

lmdb_map_size (default: 16777216)
       The initial OpenLDAP LMDB database size limit in bytes.   Each  time  a
       database becomes full, its size limit is doubled.

       This feature is available in Postfix 2.11 and later.

lmtp_address_preference (default: ipv6)
       The  LMTP-specific version of the smtp_address_preference configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_address_verify_target (default: rcpt)
       The LMTP-specific version of the smtp_address_verify_target  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 3.0 and later.

lmtp_assume_final (default: no)
       When  a  remote  LMTP  server announces no DSN support, assume that the
       server performs final delivery, and send  "delivered"  delivery  status
       notifications  instead  of  "relayed". The default setting is backwards
       compatible to avoid the infinitesimal possibility of breaking  existing
       LMTP-based content filters.

lmtp_bind_address (default: empty)
       The LMTP-specific version of the smtp_bind_address configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_bind_address6 (default: empty)
       The  LMTP-specific  version  of  the  smtp_bind_address6  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_body_checks (default: empty)
       The LMTP-specific version of the smtp_body_checks configuration parame-
       ter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_cache_connection (default: yes)
       Keep Postfix LMTP client connections open for up to $max_idle  seconds.
       When  the  LMTP  client  receives a request for the same connection the
       connection is reused.

       This parameter is available in Postfix version 2.2 and  earlier.   With
       Postfix  version  2.3  and  later, see lmtp_connection_cache_on_demand,
       lmtp_connection_cache_destinations,       or        lmtp_connection_re-
       use_time_limit.

       The  effectiveness of cached connections will be determined by the num-
       ber of remote LMTP servers in use, and the concurrency limit  specified
       for the Postfix LMTP client. Cached connections are closed under any of
       the following conditions:

             The Postfix LMTP client idle time limit is reached.  This  limit
              is  specified with the Postfix max_idle configuration parameter.

             A delivery request specifies a different  destination  than  the
              one currently cached.

             The  per-process  limit  on  the  number of delivery requests is
              reached.  This limit is specified with the Postfix max_use  con-
              figuration parameter.

             Upon  the  onset  of  another  delivery request, the remote LMTP
              server associated with the current session does not  respond  to
              the RSET command.

       Most of these limitations have been with the Postfix a connection cache
       that is shared among multiple LMTP client programs.

lmtp_cname_overrides_servername (default: yes)
       The LMTP-specific version of the  smtp_cname_overrides_servername  con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connect_timeout (default: 0s)
       The  Postfix LMTP client time limit for completing a TCP connection, or
       zero (use the operating system built-in time limit).  When  no  connec-
       tion  can  be  made within the deadline, the LMTP client tries the next
       address on the mail exchanger list.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       Example:

       lmtp_connect_timeout = 30s

lmtp_connection_cache_destinations (default: empty)
       The  LMTP-specific  version  of  the smtp_connection_cache_destinations
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_on_demand (default: yes)
       The LMTP-specific version of the  smtp_connection_cache_on_demand  con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_cache_time_limit (default: 2s)
       The  LMTP-specific version of the smtp_connection_cache_time_limit con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_connection_reuse_count_limit (default: 0)
       The LMTP-specific version of the smtp_connection_reuse_count_limit con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_connection_reuse_time_limit (default: 300s)
       The  LMTP-specific version of the smtp_connection_reuse_time_limit con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_data_done_timeout (default: 600s)
       The Postfix LMTP client time limit for sending the LMTP  ".",  and  for
       receiving  the  remote  LMTP  server  response.   When  no  response is
       received within the deadline, a warning is logged that the mail may  be
       delivered multiple times.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_data_init_timeout (default: 120s)
       The Postfix LMTP client time limit for sending the LMTP  DATA  command,
       and for receiving the remote LMTP server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_data_xfer_timeout (default: 180s)
       The Postfix LMTP client time limit for sending the  LMTP  message  con-
       tent.  When the connection stalls for more than $lmtp_data_xfer_timeout
       the LMTP client terminates the transfer.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_defer_if_no_mx_address_found (default: no)
       The LMTP-specific version of the smtp_defer_if_no_mx_address_found con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_delivery_status_filter (default: empty)
       The LMTP-specific version of the smtp_delivery_status_filter configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 3.0 and later.

lmtp_destination_concurrency_limit    (default:   $default_destination_concur-
       rency_limit)
       The maximal number of parallel deliveries to the same  destination  via
       the  lmtp  message  delivery  transport.  This limit is enforced by the
       queue manager. The message delivery transport name is the  first  field
       in the entry in the master.cf file.

lmtp_destination_recipient_limit     (default:    $default_destination_recipi-
       ent_limit)
       The maximal number of recipients  per  message  for  the  lmtp  message
       delivery  transport.  This  limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in  the
       master.cf file.

       Setting this parameter to a value of 1 changes the meaning of lmtp_des-
       tination_concurrency_limit from concurrency per domain into concurrency
       per recipient.

lmtp_discard_lhlo_keyword_address_maps (default: empty)
       Lookup  tables,  indexed  by  the remote LMTP server address, with case
       insensitive lists of LHLO keywords (pipelining, starttls,  auth,  etc.)
       that  the  Postfix  LMTP client will ignore in the LHLO response from a
       remote LMTP server. See lmtp_discard_lhlo_keywords for details. The ta-
       ble  is  not  indexed  by  hostname  for  consistency  with  smtpd_dis-
       card_ehlo_keyword_address_maps.

       This feature is available in Postfix 2.3 and later.

lmtp_discard_lhlo_keywords (default: empty)
       A case insensitive list of LHLO keywords (pipelining,  starttls,  auth,
       etc.)  that  the  Postfix  LMTP client will ignore in the LHLO response
       from a remote LMTP server.

       This feature is available in Postfix 2.3 and later.

       Notes:

             Specify the silent-discard pseudo keyword to prevent this action
              from being logged.

             Use  the  lmtp_discard_lhlo_keyword_address_maps feature to dis-
              card LHLO keywords selectively.

lmtp_dns_reply_filter (default: empty)
       Optional filter for  Postfix  LMTP  client  DNS  lookup  results.   See
       smtp_dns_reply_filter for details including an example.

       This feature is available in Postfix 3.0 and later.

lmtp_dns_resolver_options (default: empty)
       The  LMTP-specific  version of the smtp_dns_resolver_options configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.8 and later.

lmtp_dns_support_level (default: empty)
       The LMTP-specific version of the  smtp_dns_support_level  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_enforce_tls (default: no)
       The LMTP-specific version of the smtp_enforce_tls configuration parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_fallback_relay (default: empty)
       Optional list of relay hosts for LMTP destinations that can't be  found
       or  that  are unreachable.  In main.cf elements are separated by white-
       space or commas.

       By default, mail is returned to the sender when a  destination  is  not
       found, and delivery is deferred when a destination is unreachable.

       The fallback relays must be TCP destinations, specified without a lead-
       ing "inet:" prefix.  Specify a host or host:port.  Since MX lookups  do
       not  apply  with  LMTP,  there  is  no  need  to  use  the  "[host]" or
       "[host]:port" forms.  If you specify multiple LMTP destinations,  Post-
       fix will try them in the specified order.

       This feature is available in Postfix 3.1 and later.

lmtp_generic_maps (default: empty)
       The LMTP-specific version of the smtp_generic_maps configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_header_checks (default: empty)
       The  LMTP-specific  version  of  the  smtp_header_checks  configuration
       parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_host_lookup (default: dns)
       The LMTP-specific version of the smtp_host_lookup configuration parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_name (default: $myhostname)
       The hostname to send in the LMTP LHLO command.

       The default value is the  machine  hostname.   Specify  a  hostname  or
       [ip.add.re.ss].

       This  information  can  be  specified  in the main.cf file for all LMTP
       clients, or it can be specified in the master.cf file  for  a  specific
       client, for example:

           /etc/postfix/master.cf:
               mylmtp ... lmtp -o lmtp_lhlo_name=foo.bar.com

       This feature is available in Postfix 2.3 and later.

lmtp_lhlo_timeout (default: 300s)
       The  Postfix  LMTP  client time limit for sending the LHLO command, and
       for receiving the initial remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_line_length_limit (default: 990)
       The  LMTP-specific  version of the smtp_line_length_limit configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mail_timeout (default: 300s)
       The Postfix LMTP client time limit for sending the MAIL  FROM  command,
       and for receiving the remote LMTP server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_mime_header_checks (default: empty)
       The LMTP-specific version of the smtp_mime_header_checks  configuration
       parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_mx_address_limit (default: 5)
       The  LMTP-specific  version  of the smtp_mx_address_limit configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_mx_session_limit (default: 2)
       The LMTP-specific version of  the  smtp_mx_session_limit  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_nested_header_checks (default: empty)
       The  LMTP-specific  version of the smtp_nested_header_checks configura-
       tion parameter. See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_per_record_deadline (default: no)
       The LMTP-specific version of the smtp_per_record_deadline configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.9 and later.

lmtp_pix_workaround_delay_time (default: 10s)
       The LMTP-specific version of the smtp_pix_workaround_delay_time config-
       uration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workaround_maps (default: empty)
       The LMTP-specific version of the smtp_pix_workaround_maps configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.4 and later.

lmtp_pix_workaround_threshold_time (default: 500s)
       The  LMTP-specific  version  of  the smtp_pix_workaround_threshold_time
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_pix_workarounds (default: empty)
       The LMTP-specific  version  of  the  smtp_pix_workaround  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.4 and later.

lmtp_quit_timeout (default: 300s)
       The  Postfix  LMTP  client time limit for sending the QUIT command, and
       for receiving the remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_quote_rfc821_envelope (default: yes)
       The  LMTP-specific version of the smtp_quote_rfc821_envelope configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_randomize_addresses (default: yes)
       The LMTP-specific version of the smtp_randomize_addresses configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_rcpt_timeout (default: 300s)
       The Postfix LMTP client time limit for sending the RCPT TO command, and
       for receiving the remote LMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

lmtp_reply_filter (default: empty)
       The LMTP-specific version of the smtp_reply_filter configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.7 and later.

lmtp_rset_timeout (default: 20s)
       The Postfix LMTP client time limit for sending the  RSET  command,  and
       for  receiving  the  remote LMTP server response. The LMTP client sends
       RSET in order to finish a recipient address probe, or to verify that  a
       cached connection is still alive.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

lmtp_sasl_auth_cache_name (default: empty)
       The LMTP-specific version of the  smtp_sasl_auth_cache_name  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_cache_time (default: 90d)
       The  LMTP-specific  version of the smtp_sasl_auth_cache_time configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix LMTP client.

lmtp_sasl_auth_soft_bounce (default: yes)
       The LMTP-specific version of the smtp_sasl_auth_soft_bounce  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_sasl_mechanism_filter (default: empty)
       The  LMTP-specific version of the smtp_sasl_mechanism_filter configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_password_maps (default: empty)
       Optional Postfix LMTP client lookup tables with  one  username:password
       entry  per  host  or  domain.   If a remote host or domain has no user-
       name:password entry, then the Postfix LMTP client will not  attempt  to
       authenticate to the remote host.

lmtp_sasl_path (default: empty)
       Implementation-specific  information that is passed through to the SASL
       plug-in implementation that is selected with lmtp_sasl_type.  Typically
       this specifies the name of a configuration file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_security_options (default: noplaintext, noanonymous)
       SASL security options; as of Postfix 2.3 the list of available features
       depends on  the  SASL  client  implementation  that  is  selected  with
       lmtp_sasl_type.

       The  following  security features are defined for the cyrus client SASL
       implementation:

       noplaintext
              Disallow authentication methods that use plaintext passwords.

       noactive
              Disallow authentication methods that are vulnerable to  non-dic-
              tionary active attacks.

       nodictionary
              Disallow  authentication  methods that are vulnerable to passive
              dictionary attack.

       noanonymous
              Disallow anonymous logins.

       Example:

       lmtp_sasl_security_options = noplaintext

lmtp_sasl_tls_security_options (default: $lmtp_sasl_security_options)
       The LMTP-specific version of the smtp_sasl_tls_security_options config-
       uration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_tls_verified_security_options     (default:     $lmtp_sasl_tls_secu-
       rity_options)
       The   LMTP-specific   version   of   the   smtp_sasl_tls_verified_secu-
       rity_options configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_sasl_type (default: cyrus)
       The  SASL  plug-in  type  that  the  Postfix LMTP client should use for
       authentication.  The available types are listed with the "postconf  -A"
       command.

       This feature is available in Postfix 2.3 and later.

lmtp_send_dummy_mail_auth (default: no)
       The  LMTP-specific  version of the smtp_send_dummy_mail_auth configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.9 and later.

lmtp_send_xforward_command (default: no)
       Send an XFORWARD command to the remote LMTP server when the  LMTP  LHLO
       server  response  announces  XFORWARD  support.  This allows an lmtp(8)
       delivery agent, used for content filter message injection,  to  forward
       the name, address, protocol and HELO name of the original client to the
       content filter and downstream queuing LMTP server.  Before  you  change
       the value to yes, it is best to make sure that your content filter sup-
       ports this command.

       This feature is available in Postfix 2.1 and later.

lmtp_sender_dependent_authentication (default: no)
       The LMTP-specific version of  the  smtp_sender_dependent_authentication
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_5xx_greeting (default: yes)
       The  LMTP-specific  version of the smtp_skip_5xx_greeting configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_skip_quit_response (default: no)
       Wait for the response to the LMTP QUIT command.

lmtp_starttls_timeout (default: 300s)
       The LMTP-specific version of  the  smtp_starttls_timeout  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tcp_port (default: 24)
       The default TCP port that the Postfix LMTP client connects to.

lmtp_tls_CAfile (default: empty)
       The  LMTP-specific version of the smtp_tls_CAfile configuration parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_CApath (default: empty)
       The LMTP-specific version of the smtp_tls_CApath configuration  parame-
       ter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_block_early_mail_reply (default: empty)
       The  LMTP-specific  version of the smtp_tls_block_early_mail_reply con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.7 and later.

lmtp_tls_cert_file (default: empty)
       The  LMTP-specific  version  of  the  smtp_tls_cert_file  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_ciphers (default: medium)
       The LMTP-specific version of the smtp_tls_ciphers configuration parame-
       ter. See there for details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_dcert_file (default: empty)
       The LMTP-specific  version  of  the  smtp_tls_dcert_file  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_dkey_file (default: $lmtp_tls_dcert_file)
       The  LMTP-specific  version  of  the  smtp_tls_dkey_file  configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_eccert_file (default: empty)
       The LMTP-specific version  of  the  smtp_tls_eccert_file  configuration
       parameter.  See there for details.

       This  feature  is  available  in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

lmtp_tls_eckey_file (default: empty)
       The LMTP-specific  version  of  the  smtp_tls_eckey_file  configuration
       parameter.  See there for details.

       This  feature  is  available  in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

lmtp_tls_enforce_peername (default: yes)
       The LMTP-specific version of the  smtp_tls_enforce_peername  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_exclude_ciphers (default: empty)
       The LMTP-specific version of the smtp_tls_exclude_ciphers configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_fingerprint_cert_match (default: empty)
       The LMTP-specific version of the  smtp_tls_fingerprint_cert_match  con-
       figuration parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_fingerprint_digest (default: md5)
       The LMTP-specific version of the smtp_tls_fingerprint_digest configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.5 and later.

lmtp_tls_force_insecure_host_tlsa_lookup (default: no)
       The    LMTP-specific    version     of     the     smtp_tls_force_inse-
       cure_host_tlsa_lookup  configuration parameter.  See there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_tls_key_file (default: $lmtp_tls_cert_file)
       The LMTP-specific version of the smtp_tls_key_file configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_loglevel (default: 0)
       The LMTP-specific version of the smtp_tls_loglevel configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_ciphers (default: medium)
       The LMTP-specific version of the smtp_tls_mandatory_ciphers  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_exclude_ciphers (default: empty)
       The  LMTP-specific  version  of  the smtp_tls_mandatory_exclude_ciphers
       configuration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_mandatory_protocols (default: !SSLv2, !SSLv3)
       The LMTP-specific version of the smtp_tls_mandatory_protocols  configu-
       ration parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_note_starttls_offer (default: no)
       The  LMTP-specific version of the smtp_tls_note_starttls_offer configu-
       ration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_per_site (default: empty)
       The LMTP-specific version of the smtp_tls_per_site configuration param-
       eter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_policy_maps (default: empty)
       The  LMTP-specific  version  of  the smtp_tls_policy_maps configuration
       parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_protocols (default: !SSLv2, !SSLv3)
       The  LMTP-specific  version  of  the  smtp_tls_protocols  configuration
       parameter. See there for details.

       This feature is available in Postfix 2.6 and later.

lmtp_tls_scert_verifydepth (default: 9)
       The  LMTP-specific version of the smtp_tls_scert_verifydepth configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_secure_cert_match (default: nexthop)
       The LMTP-specific version of the smtp_tls_secure_cert_match  configura-
       tion parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_security_level (default: empty)
       The  LMTP-specific version of the smtp_tls_security_level configuration
       parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_database (default: empty)
       The LMTP-specific version of the  smtp_tls_session_cache_database  con-
       figuration parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_session_cache_timeout (default: 3600s)
       The LMTP-specific version of the smtp_tls_session_cache_timeout config-
       uration parameter.  See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_tls_trust_anchor_file (default: empty)
       The LMTP-specific version of the smtp_tls_trust_anchor_file  configura-
       tion parameter.  See there for details.

       This feature is available in Postfix 2.11 and later.

lmtp_tls_verify_cert_match (default: hostname)
       The  LMTP-specific version of the smtp_tls_verify_cert_match configura-
       tion parameter. See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_use_tls (default: no)
       The LMTP-specific version of the smtp_use_tls configuration  parameter.
       See there for details.

       This feature is available in Postfix 2.3 and later.

lmtp_xforward_timeout (default: 300s)
       The  Postfix  LMTP  client time limit for sending the XFORWARD command,
       and for receiving the remote LMTP server response.

       In case of problems the client does NOT try the  next  address  on  the
       mail exchanger list.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

local_command_shell (default: empty)
       Optional shell program for local(8) delivery  to  non-Postfix  command.
       By  default,  non-Postfix  commands are executed directly; commands are
       given to given to the default shell (typically, /bin/sh) only when they
       contain shell meta characters or shell built-in commands.

       "sendmail's  restricted  shell" (smrsh) is what most people will use in
       order to restrict what programs can be run  from  e.g.  .forward  files
       (smrsh is part of the Sendmail distribution).

       Note:  when  a  shell program is specified, it is invoked even when the
       command contains no shell built-in commands or meta characters.

       Example:

       local_command_shell = /some/where/smrsh -c
       local_command_shell = /bin/bash -c

local_delivery_status_filter (default: $default_delivery_status_filter)
       Optional filter for the local(8) delivery agent to  change  the  status
       code or explanatory text of successful or unsuccessful deliveries.  See
       default_delivery_status_filter for details.

       This feature is available in Postfix 3.0 and later.

local_destination_concurrency_limit (default: 2)
       The maximal number of parallel deliveries via the local  mail  delivery
       transport   to  the  same  recipient  (when  "local_destination_recipi-
       ent_limit = 1") or the maximal number of  parallel  deliveries  to  the
       same  local domain (when "local_destination_recipient_limit > 1"). This
       limit is enforced by the queue manager. The message delivery  transport
       name is the first field in the entry in the master.cf file.

       A  low limit of 2 is recommended, just in case someone has an expensive
       shell command in a .forward file or in an alias (e.g., a  mailing  list
       manager).  You don't want to run lots of those at the same time.

local_destination_recipient_limit (default: 1)
       The  maximal  number  of  recipients per message delivery via the local
       mail delivery transport. This limit is enforced by the  queue  manager.
       The  message delivery transport name is the first field in the entry in
       the master.cf file.

       Setting this parameter to a value > 1 changes the meaning of local_des-
       tination_concurrency_limit  from concurrency per recipient into concur-
       rency per domain.

local_header_rewrite_clients (default: permit_inet_interfaces)
       Rewrite message header addresses in mail from these clients and  update
       incomplete  addresses  with  the domain name in $myorigin or $mydomain;
       either don't rewrite message headers from other clients at all, or  re-
       write  message  headers and update incomplete addresses with the domain
       specified in the remote_header_rewrite_domain parameter.

       See  the  append_at_myorigin  and  append_dot_mydomain  parameters  for
       details of how domain names are appended to incomplete addresses.

       Specify a list of zero or more of the following:

       permit_inet_interfaces
              Append the domain name in $myorigin or $mydomain when the client
              IP address matches $inet_interfaces. This is enabled by default.

       permit_mynetworks
              Append the domain name in $myorigin or $mydomain when the client
              IP address matches any network  or  network  address  listed  in
              $mynetworks.  This  setting  will not prevent remote mail header
              address rewriting when mail from a remote client is forwarded by
              a neighboring system.

       permit_sasl_authenticated
              Append the domain name in $myorigin or $mydomain when the client
              is successfully authenticated via the RFC 4954 (AUTH)  protocol.

       permit_tls_clientcerts
              Append the domain name in $myorigin or $mydomain when the remote
              SMTP client TLS certificate fingerprint or  public  key  finger-
              print  (Postfix  2.9 and later) is listed in $relay_clientcerts.
              The  fingerprint  digest  algorithm  is  configurable  via   the
              smtpd_tls_fingerprint_digest  parameter (hard-coded as md5 prior
              to Postfix version 2.5).

       permit_tls_all_clientcerts
              Append the domain name in $myorigin or $mydomain when the remote
              SMTP client TLS certificate is successfully verified, regardless
              of whether it is listed on the server,  and  regardless  of  the
              certifying authority.

       check_address_map type:table

       type:table
              Append the domain name in $myorigin or $mydomain when the client
              IP address matches  the  specified  lookup  table.   The  lookup
              result  is  ignored, and no subnet lookup is done. This is suit-
              able for, e.g., pop-before-smtp lookup tables.

       Examples:

       The Postfix < 2.2 backwards compatible setting: always rewrite  message
       headers,   and  always  append  my  own  domain  to  incomplete  header
       addresses.

           local_header_rewrite_clients = static:all

       The purist (and default) setting: rewrite headers  only  in  mail  from
       Postfix sendmail and in SMTP mail from this machine.

           local_header_rewrite_clients = permit_inet_interfaces

       The intermediate setting: rewrite header addresses and append $myorigin
       or $mydomain information only with mail  from  Postfix  sendmail,  from
       local clients, or from authorized SMTP clients.

       Note:  this setting will not prevent remote mail header address rewrit-
       ing when mail from a remote client is forwarded by a  neighboring  sys-
       tem.

           local_header_rewrite_clients = permit_mynetworks,
               permit_sasl_authenticated permit_tls_clientcerts
               check_address_map hash:/etc/postfix/pop-before-smtp

local_recipient_maps (default: proxy:unix:passwd.byname $alias_maps)
       Lookup tables with all names or addresses of local recipients: a recip-
       ient  address  is  local  when  its  domain   matches   $mydestination,
       $inet_interfaces  or $proxy_interfaces.  Specify @domain as a wild-card
       for domains that do not have  a  valid  recipient  list.   Technically,
       tables  listed  with  $local_recipient_maps  are used as lists: Postfix
       needs to know only if a lookup string is found or not, but it does  not
       use the result from table lookup.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       If  this  parameter  is  non-empty (the default), then the Postfix SMTP
       server will reject mail for unknown local users.

       To turn off local recipient checking in the Postfix SMTP server,  spec-
       ify "local_recipient_maps =" (i.e. empty).

       The  default  setting  assumes  that  you use the default Postfix local
       delivery agent for local delivery. You need to update the local_recipi-
       ent_maps setting if:

             You redefine the local delivery agent in master.cf.

             You redefine the "local_transport" setting in main.cf.

             You   use  the  "luser_relay",  "mailbox_transport",  or  "fall-
              back_transport" feature of the Postfix local(8) delivery  agent.

       Details are described in the LOCAL_RECIPIENT_README file.

       Beware:  if  the  Postfix SMTP server runs chrooted, you need to access
       the passwd file via the  proxymap(8)  service,  in  order  to  overcome
       chroot  access restrictions. The alternative, maintaining a copy of the
       system password file in the chroot jail is not practical.

       Examples:

       local_recipient_maps =

local_transport (default: local:$myhostname)
       The default mail delivery transport and next-hop destination for  final
       delivery to domains listed with mydestination, and for [ipaddress] des-
       tinations  that  match  $inet_interfaces  or  $proxy_interfaces.   This
       information can be overruled with the transport(5) table.

       By  default,  local  mail is delivered to the transport called "local",
       which is just the name of a service that is defined the master.cf file.

       Specify  a string of the form transport:nexthop, where transport is the
       name of a mail delivery transport defined in master.cf.   The  :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       Beware: if you override the default local delivery agent then you  need
       to  review  the  LOCAL_RECIPIENT_README  document,  otherwise  the SMTP
       server may reject mail for local recipients.

luser_relay (default: empty)
       Optional catch-all destination for  unknown  local(8)  recipients.   By
       default,  mail for unknown recipients in domains that match $mydestina-
       tion, $inet_interfaces or $proxy_interfaces is returned  as  undeliver-
       able.

       The following $name expansions are done on luser_relay:

       $domain
              The recipient domain.

       $extension
              The recipient address extension.

       $home  The recipient's home directory.

       $local The entire recipient address localpart.

       $recipient
              The full recipient address.

       $recipient_delimiter
              The  address extension delimiter that was found in the recipient
              address (Postfix 2.11 and later), or the  system-wide  recipient
              address extension delimiter (Postfix 2.10 and earlier).

       $shell The recipient's login shell.

       $user  The recipient username.

       ${name?value}
              Expands to value when $name has a non-empty value.

       ${name:value}
              Expands to value when $name has an empty value.

       Instead of $name you can also specify ${name} or $(name).

       Note: luser_relay works only for the Postfix local(8) delivery agent.

       Note:  if  you  use  this feature for accounts not in the UNIX password
       file, then you must specify "local_recipient_maps ="  (i.e.  empty)  in
       the  main.cf  file,  otherwise the Postfix SMTP server will reject mail
       for non-UNIX accounts with "User unknown in local recipient table".

       Examples:

       luser_relay = $user@other.host
       luser_relay = $local@other.host
       luser_relay = admin+$local

mail_name (default: Postfix)
       The mail system name that is displayed in  Received:  headers,  in  the
       SMTP greeting banner, and in bounced mail.

mail_owner (default: postfix)
       The  UNIX  system  account that owns the Postfix queue and most Postfix
       daemon processes.  Specify the name of  an  unprivileged  user  account
       that  does  not  share a user or group ID with other accounts, and that
       owns no other files or processes on the system.  In  particular,  don't
       specify nobody or daemon.  PLEASE USE A DEDICATED USER ID AND GROUP ID.

       When this parameter value  is  changed  you  need  to  re-run  "postfix
       set-permissions"  (with  Postfix  version  2.0 and earlier: "/etc/post-
       fix/post-install set-permissions".

mail_release_date (default: see postconf -d output)
       The Postfix release date, in "YYYYMMDD" format.

mail_spool_directory (default: see postconf -d output)
       The directory where local(8) UNIX-style mailboxes are kept. The default
       setting  depends  on  the  system  type. Specify a name ending in / for
       maildir-style delivery.

       Note: maildir delivery is done with the privileges  of  the  recipient.
       If you use the mail_spool_directory setting for maildir style delivery,
       then you must create the top-level maildir directory in advance.  Post-
       fix will not create it.

       Examples:

       mail_spool_directory = /var/mail
       mail_spool_directory = /var/spool/mail

mail_version (default: see postconf -d output)
       The   version   of   the   mail   system.  Stable  releases  are  named
       major.minor.patchlevel. Experimental releases also include the  release
       date. The version string can be used in, for example, the SMTP greeting
       banner.

mailbox_command (default: empty)
       Optional external command that the local(8) delivery agent  should  use
       for mailbox delivery.  The command is run with the user ID and the pri-
       mary group ID privileges of the recipient.  Exception: command delivery
       for  root executes with $default_privs privileges.  This is not a prob-
       lem, because 1) mail for root should always be aliased to a  real  user
       and 2) don't log in as root, use "su" instead.

       The following environment variables are exported to the command:

       CLIENT_ADDRESS
              Remote  client network address. Available in Postfix version 2.2
              and later.

       CLIENT_HELO
              Remote client EHLO command parameter. Available in Postfix  ver-
              sion 2.2 and later.

       CLIENT_HOSTNAME
              Remote  client  hostname.  Available  in Postfix version 2.2 and
              later.

       CLIENT_PROTOCOL
              Remote client protocol. Available in  Postfix  version  2.2  and
              later.

       DOMAIN The domain part of the recipient address.

       EXTENSION
              The optional address extension.

       HOME   The recipient home directory.

       LOCAL  The recipient address localpart.

       LOGNAME
              The recipient's username.

       ORIGINAL_RECIPIENT
              The  entire  recipient  address, before any address rewriting or
              aliasing.

       RECIPIENT
              The full recipient address.

       SASL_METHOD
              SASL authentication method specified in the remote  client  AUTH
              command. Available in Postfix version 2.2 and later.

       SASL_SENDER
              SASL  sender  address  specified  in the remote client MAIL FROM
              command. Available in Postfix version 2.2 and later.

       SASL_USER
              SASL username specified  in  the  remote  client  AUTH  command.
              Available in Postfix version 2.2 and later.

       SENDER The full sender address.

       SHELL  The recipient's login shell.

       USER   The recipient username.

       Unlike  other  Postfix  configuration  parameters,  the mailbox_command
       parameter is not subjected to $name substitutions. This is to  make  it
       easier to specify shell syntax (see example below).

       If you can, avoid shell meta characters because they will force Postfix
       to run an expensive shell process. If you're  delivering  via  Procmail
       then  running  a  shell won't make a noticeable difference in the total
       cost.

       Note: if you use the  mailbox_command  feature  to  deliver  mail  sys-
       tem-wide,  you  must  set  up an alias that forwards mail for root to a
       real user.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       Examples:

       mailbox_command = /some/where/procmail
       mailbox_command = /some/where/procmail -a "$EXTENSION"
       mailbox_command = /some/where/maildrop -d "$USER"
               -f "$SENDER" "$EXTENSION"

mailbox_command_maps (default: empty)
       Optional  lookup tables with per-recipient external commands to use for
       local(8) mailbox delivery.  Behavior is as with mailbox_command.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

mailbox_delivery_lock (default: see postconf -d output)
       How  to  lock a UNIX-style local(8) mailbox before attempting delivery.
       For a list of available file locking methods,  use  the  "postconf  -l"
       command.

       This  setting  is  ignored  with  maildir  style delivery, because such
       deliveries are safe without explicit locks.

       Note: The dotlock method requires that the recipient  UID  or  GID  has
       write access to the parent directory of the mailbox file.

       Note: the default setting of this parameter is system dependent.

mailbox_size_limit (default: 51200000)
       The maximal size of any local(8) individual mailbox or maildir file, or
       zero (no limit).  In fact, this limits the size of  any  file  that  is
       written  to  upon  local  delivery, including files written by external
       commands that are executed by the local(8) delivery agent.

       This limit must not be smaller than the message size limit.

mailbox_transport (default: empty)
       Optional message delivery transport that the  local(8)  delivery  agent
       should use for mailbox delivery to all local recipients, whether or not
       they are found in the UNIX passwd database.

       The precedence of local(8) delivery  features  from  high  to  low  is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps, mailbox_command, home_mailbox,  mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

mailbox_transport_maps (default: empty)
       Optional  lookup  tables with per-recipient message delivery transports
       to use for local(8) mailbox delivery, whether or not the recipients are
       found in the UNIX passwd database.

       The  precedence  of  local(8)  delivery  features  from high to low is:
       aliases,  .forward  files,  mailbox_transport_maps,  mailbox_transport,
       mailbox_command_maps,  mailbox_command, home_mailbox, mail_spool_direc-
       tory, fallback_transport_maps, fallback_transport and luser_relay.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       For safety reasons, this feature does not allow  $number  substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

mailq_path (default: see postconf -d output)
       Sendmail   compatibility  feature  that  specifies  where  the  Postfix
       mailq(1) command is installed. This command can be  used  to  list  the
       Postfix mail queue.

manpage_directory (default: see postconf -d output)
       Where the Postfix manual pages are installed.

maps_rbl_domains (default: empty)
       Obsolete feature: use the reject_rbl_client feature instead.

maps_rbl_reject_code (default: 554)
       The  numerical  Postfix  SMTP  server  response code when a remote SMTP
       client    request    is    blocked    by     the     reject_rbl_client,
       reject_rhsbl_client,  reject_rhsbl_reverse_client,  reject_rhsbl_sender
       or reject_rhsbl_recipient restriction.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

masquerade_classes (default: envelope_sender, header_sender, header_recipient)

       What addresses are subject to address masquerading.

       By  default,  address  masquerading  is  limited  to  envelope   sender
       addresses,  and  to header sender and header recipient addresses.  This
       allows you to use address masquerading on a mail  gateway  while  still
       being able to forward mail to users on individual machines.

       Specify   zero   or   more   of:  envelope_sender,  envelope_recipient,
       header_sender, header_recipient

masquerade_domains (default: empty)
       Optional list of domains whose subdomain structure will be stripped off
       in email addresses.

       The  list is processed left to right, and processing stops at the first
       match.  Thus,

           masquerade_domains = foo.example.com example.com

       strips "user@any.thing.foo.example.com" to "user@foo.example.com",  but
       strips "user@any.thing.else.example.com" to "user@example.com".

       A  domain  name  prefixed with ! means do not masquerade this domain or
       its subdomains. Thus,

           masquerade_domains = !foo.example.com example.com

       does not  change  "user@any.thing.foo.example.com"  or  "user@foo.exam-
       ple.com",  but  strips "user@any.thing.else.example.com" to "user@exam-
       ple.com".

       Note: with Postfix version 2.2,  message  header  address  masquerading
       happens only when message header address rewriting is enabled:

             The message is received with the Postfix sendmail(1) command,

             The  message  is  received  from  a  network client that matches
              $local_header_rewrite_clients,

             The  message   is   received   from   the   network,   and   the
              remote_header_rewrite_domain  parameter  specifies  a  non-empty
              value.

       To   get   the   behavior   before   Postfix   version   2.2,   specify
       "local_header_rewrite_clients = static:all".

       Example:

       masquerade_domains = $mydomain

masquerade_exceptions (default: empty)
       Optional  list  of  user  names  that are not subjected to address mas-
       querading, even when their address matches $masquerade_domains.

       By default, address masquerading makes no exceptions.

       Specify a list of user names, "/file/name"  or  "type:table"  patterns,
       separated  by  commas  and/or  whitespace.  The list is matched left to
       right, and the search stops on the first match. A "/file/name"  pattern
       is  replaced  by  its  contents; a "type:table" lookup table is matched
       when a name matches a lookup key (the lookup result is ignored).   Con-
       tinue  long  lines  by  starting the next line with whitespace. Specify
       "!pattern" to exclude a name from the list. The form  "!/file/name"  is
       supported only in Postfix version 2.4 and later.

       Examples:

       masquerade_exceptions = root, mailer-daemon
       masquerade_exceptions = root

master_service_disable (default: empty)
       Selectively disable master(8) listener ports by service type or by ser-
       vice name and type.  Specify a list of service types  ("inet",  "unix",
       "fifo",  or  "pass")  or  "name/type" tuples, where "name" is the first
       field of a master.cf entry and "type" is a service type. As with  other
       Postfix  matchlists, a search stops at the first match.  Specify "!pat-
       tern" to exclude a service from the list.  By  default,  all  master(8)
       listener ports are enabled.

       Note:  this  feature does not support "/file/name" or "type:table" pat-
       terns, nor does it support wildcards such as  "*"  or  "all".  This  is
       intentional.

       Examples:

       # With Postfix 2.6..2.10 use '.' instead of '/'.
       # Turn on all master(8) listener ports (the default).
       master_service_disable =
       # Turn off only the main SMTP listener port.
       master_service_disable = smtp/inet
       # Turn off all TCP/IP listener ports.
       master_service_disable = inet
       # Turn off all TCP/IP listener ports except "foo".
       master_service_disable = !foo/inet, inet

       This feature is available in Postfix 2.6 and later.

max_idle (default: 100s)
       The  maximum  amount  of time that an idle Postfix daemon process waits
       for an incoming connection before terminating voluntarily.  This param-
       eter  is  ignored  by the Postfix queue manager and by other long-lived
       Postfix daemon processes.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

max_use (default: 100)
       The  maximal  number  of  incoming  connections  that  a Postfix daemon
       process will service before terminating voluntarily.  This parameter is
       ignored  by  the  Postfix queue manager and by other long-lived Postfix
       daemon processes.

maximal_backoff_time (default: 4000s)
       The maximal time between attempts to deliver a deferred message.

       This parameter should be set to a value greater than or equal to $mini-
       mal_backoff_time. See also $queue_run_delay.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

maximal_queue_lifetime (default: 5d)
       Consider a message as undeliverable, when delivery fails with a  tempo-
       rary   error,  and  the  time  in  the  queue  has  reached  the  maxi-
       mal_queue_lifetime limit.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is d (days).

       Specify 0 when mail delivery should be tried only once.

message_drop_headers (default: bcc, content-length, resent-bcc, return-path)
       Names  of  message headers that the cleanup(8) daemon will remove after
       applying header_checks(5) and before invoking Milter applications.  The
       default setting is compatible with Postfix < 3.0.

       Specify a list of header names, separated by comma or space.  Names are
       matched in a case-insensitive manner.  The  list  of  supported  header
       names is limited only by available memory.

       This feature is available in Postfix 3.0 and later.

message_reject_characters (default: empty)
       The set of characters that Postfix will reject in message content.  The
       usual C-like escape sequences are recognized: \a \b \f \n \r \t \v \ddd
       (up to three octal digits) and \\.

       Note  1: this feature does not recognize text that requires MIME decod-
       ing. It inspects raw  message  content,  just  like  header_checks  and
       body_checks.

       Note  2:  this  feature  is  disabled  with "receive_override_options =
       no_header_body_checks".

       Example:

       message_reject_characters = \0

       This feature is available in Postfix 2.3 and later.

message_size_limit (default: 10240000)
       The maximal size in bytes of a message, including envelope information.

       Note:  be  careful  when making changes.  Excessively small values will
       result in the loss of non-delivery notifications, when a bounce message
       size exceeds the local or remote MTA's message size limit.

message_strip_characters (default: empty)
       The  set  of  characters that Postfix will remove from message content.
       The usual C-like escape sequences are recognized: \a \b \f \n \r \t  \v
       \ddd (up to three octal digits) and \\.

       Note  1: this feature does not recognize text that requires MIME decod-
       ing. It inspects raw  message  content,  just  like  header_checks  and
       body_checks.

       Note  2:  this  feature  is  disabled  with "receive_override_options =
       no_header_body_checks".

       Example:

       message_strip_characters = \0

       This feature is available in Postfix 2.3 and later.

meta_directory (default: see 'postconf -d' output)
       The location of non-executable files that  are  shared  among  multiple
       Postfix  instances,  such  as  postfix-files,  dynamicmaps.cf,  and the
       multi-instance template files main.cf.proto and master.cf.proto.   This
       directory  should  contain  only Postfix-related files.  Typically, the
       meta_directory parameter has the same default as  the  config_directory
       parameter (/etc/postfix or /usr/local/etc/postfix).

       For  backwards  compatibility  with Postfix versions 2.6..2.11, specify
       "meta_directory = $daemon_directory" in main.cf  before  installing  or
       upgrading  Postfix,  or  specify  "meta_directory  = /path/name" on the
       "make makefiles", "make install" or "make upgrade" command line.

       This feature is available in Postfix 3.0 and later.

milter_command_timeout (default: 30s)
       The time limit for sending an SMTP command to a  Milter  (mail  filter)
       application, and for receiving the response.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_connect_macros (default: see postconf -d output)
       The  macros  that  are  sent to Milter (mail filter) applications after
       completion of an SMTP connection.  See  MILTER_README  for  a  list  of
       available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_connect_timeout (default: 30s)
       The  time  limit  for connecting to a Milter (mail filter) application,
       and for negotiating protocol options.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter suffix that specifies the time unit).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_content_timeout (default: 300s)
       The time limit for sending message content to a  Milter  (mail  filter)
       application, and for receiving the response.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.3 and later.

milter_data_macros (default: see postconf -d output)
       The  macros  that  are sent to version 4 or higher Milter (mail filter)
       applications after the SMTP DATA command. See MILTER_README for a  list
       of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_default_action (default: tempfail)
       The  default action when a Milter (mail filter) application is unavail-
       able or mis-configured. Specify one of the following:

       accept Proceed as if the mail filter was not present.

       reject Reject all further commands in this  session  with  a  permanent
              status code.

       tempfail
              Reject  all  further  commands  in this session with a temporary
              status code.

       quarantine
              Like "accept", but freeze  the  message  in  the  "hold"  queue.
              Available with Postfix 2.6 and later.

       This feature is available in Postfix 2.3 and later.

milter_end_of_data_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       message end-of-data. See MILTER_README for a list  of  available  macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_end_of_header_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       end of the message header. See MILTER_README for a  list  of  available
       macro names and their meanings.

       This feature is available in Postfix 2.5 and later.

milter_header_checks (default: empty)
       Optional  lookup  tables for content inspection of message headers that
       are produced by Milter applications.  See the  header_checks(5)  manual
       page available actions. Currently, PREPEND is not implemented.

       The  following  example sends all mail that is marked as SPAM to a spam
       handling machine. Note that matches are case-insensitive by default.

       /etc/postfix/main.cf:
           milter_header_checks = pcre:/etc/postfix/milter_header_checks

       /etc/postfix/milter_header_checks:
           /^X-SPAM-FLAG:\s+YES/ FILTER mysmtp:sanitizer.example.com:25

       The milter_header_checks mechanism could also be used for whitelisting.
       For  example  it  could  be  used  to skip heavy content inspection for
       DKIM-signed mail from known friendly domains.

       This feature is available in Postfix 2.7, and as an optional patch  for
       Postfix 2.6.

milter_helo_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP HELO or EHLO command. See MILTER_README for a  list  of  available
       macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_macro_daemon_name (default: $myhostname)
       The  {daemon_name}  macro  value for Milter (mail filter) applications.
       See MILTER_README for a list of available macro names and  their  mean-
       ings.

       This feature is available in Postfix 2.3 and later.

milter_macro_defaults (default: empty)
       Optional list of name=value pairs that specify default values for arbi-
       trary macros that Postfix  may  send  to  Milter  applications.   These
       defaults  are  used when there is no corresponding information from the
       message delivery context.

       Specify name=value or {name}=value pairs separated by comma  or  white-
       space.   Enclose  a  pair in "{}" when a value contains comma or white-
       space (this form ignores whitespace after the enclosing "{", around the
       "=", and before the enclosing "}").

       This feature is available in Postfix 3.1 and later.

milter_macro_v (default: $mail_name $mail_version)
       The  {v}  macro  value for Milter (mail filter) applications.  See MIL-
       TER_README for a list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_mail_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP MAIL FROM command. See MILTER_README for a list of available macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_protocol (default: 6)
       The mail filter protocol version and optional protocol  extensions  for
       communication  with  a  Milter  application;  prior  to Postfix 2.6 the
       default protocol is 2. Postfix sends this  version  number  during  the
       initial protocol handshake.  It should match the version number that is
       expected by the mail filter application (or by its Milter library).

       Protocol versions:

       2      Use Sendmail 8 mail filter  protocol  version  2  (default  with
              Sendmail  version 8.11 .. 8.13 and Postfix version 2.3 ..  2.5).

       3      Use Sendmail 8 mail filter protocol version 3.

       4      Use Sendmail 8 mail filter protocol version 4.

       6      Use Sendmail 8 mail filter  protocol  version  6  (default  with
              Sendmail version 8.14 and Postfix version 2.6).

       Protocol extensions:

       no_header_reply
              Specify this when the Milter application will not reply for each
              individual message header.

       This feature is available in Postfix 2.3 and later.

milter_rcpt_macros (default: see postconf -d output)
       The macros that are sent to Milter (mail filter) applications after the
       SMTP  RCPT  TO command. See MILTER_README for a list of available macro
       names and their meanings.

       This feature is available in Postfix 2.3 and later.

milter_unknown_command_macros (default: see postconf -d output)
       The macros that are sent to version 3 or higher  Milter  (mail  filter)
       applications  after  an  unknown SMTP command.  See MILTER_README for a
       list of available macro names and their meanings.

       This feature is available in Postfix 2.3 and later.

mime_boundary_length_limit (default: 2048)
       The maximal length of MIME multipart boundary strings. The MIME proces-
       sor  is unable to distinguish between boundary strings that do not dif-
       fer in the first $mime_boundary_length_limit characters.

       This feature is available in Postfix 2.0 and later.

mime_header_checks (default: $header_checks)
       Optional lookup tables for content inspection of MIME  related  message
       headers, as described in the header_checks(5) manual page.

       This feature is available in Postfix 2.0 and later.

mime_nesting_limit (default: 100)
       The maximal recursion level that the MIME processor will handle.  Post-
       fix refuses mail that is nested deeper than the specified limit.

       This feature is available in Postfix 2.0 and later.

minimal_backoff_time (default: 300s)
       The minimal time between attempts to deliver a deferred message;  prior
       to Postfix 2.4 the default value was 1000s.

       This  parameter also limits the time an unreachable destination is kept
       in the short-term, in-memory, destination status cache.

       This parameter should be set greater than or equal to $queue_run_delay.
       See also $maximal_backoff_time.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

multi_instance_directories (default: empty)
       An optional list  of  non-default  Postfix  configuration  directories;
       these directories belong to additional Postfix instances that share the
       Postfix executable files and documentation  with  the  default  Postfix
       instance,  and  that  are  started,  stopped,  etc.,  together with the
       default Postfix instance.  Specify a list  of  pathnames  separated  by
       comma or whitespace.

       When  $multi_instance_directories is empty, the postfix(1) command runs
       in single-instance mode and operates on a single Postfix instance only.
       Otherwise,  the  postfix(1)  command  runs  in  multi-instance mode and
       invokes    the    multi-instance    manager    specified    with    the
       multi_instance_wrapper  parameter.  The  multi-instance manager in turn
       executes postfix(1) commands for the default instance and for all Post-
       fix instances in $multi_instance_directories.

       Currently,  this  parameter  setting  is ignored except for the default
       main.cf file.

       This feature is available in Postfix 2.6 and later.

multi_instance_enable (default: no)
       Allow this  Postfix  instance  to  be  started,  stopped,  etc.,  by  a
       multi-instance  manager.   By  default,  new instances are created in a
       safe state that prevents them from being started  inadvertently.   This
       parameter is reserved for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_group (default: empty)
       The  optional  instance  group  name  of this Postfix instance. A group
       identifies closely-related Postfix instances  that  the  multi-instance
       manager  can  start, stop, etc., as a unit.  This parameter is reserved
       for the multi-instance manager.

       This feature is available in Postfix 2.6 and later.

multi_instance_name (default: empty)
       The optional instance name of this Postfix instance. This name  becomes
       also the default value for the syslog_name parameter.

       This feature is available in Postfix 2.6 and later.

multi_instance_wrapper (default: empty)
       The  pathname  of  a multi-instance manager command that the postfix(1)
       command invokes when the multi_instance_directories parameter value  is
       non-empty.  The  pathname  may be followed by initial command arguments
       separated by whitespace; shell metacharacters such as  quotes  are  not
       supported in this context.

       The  postfix(1) command invokes the manager command with the postfix(1)
       non-option command arguments on the manager command line, and with  all
       installation configuration parameters exported into the manager command
       process environment. The manager command in turn invokes the postfix(1)
       command  for  individual Postfix instances as "postfix -c config_direc-
       tory command".

       This feature is available in Postfix 2.6 and later.

multi_recipient_bounce_reject_code (default: 550)
       The numerical Postfix SMTP server response  code  when  a  remote  SMTP
       client request is blocked by the reject_multi_recipient_bounce restric-
       tion.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

       This feature is available in Postfix 2.1 and later.

mydestination (default: $myhostname, localhost.$mydomain, localhost)
       The  list  of  domains that are delivered via the $local_transport mail
       delivery transport. By default this is the  Postfix  local(8)  delivery
       agent  which  looks  up all recipients in /etc/passwd and /etc/aliases.
       The SMTP  server  validates  recipient  addresses  with  $local_recipi-
       ent_maps and rejects non-existent recipients. See also the local domain
       class in the ADDRESS_CLASS_README file.

       The default mydestination value specifies names for the  local  machine
       only.  On a mail domain gateway, you should also include $mydomain.

       The   $local_transport  delivery  method  is  also  selected  for  mail
       addressed to user@[the.net.work.address] of the  mail  system  (the  IP
       addresses  specified  with  the  inet_interfaces  and  proxy_interfaces
       parameters).

       Warnings:

             Do not specify the names of virtual domains - those domains  are
              specified elsewhere. See VIRTUAL_README for more information.

             Do  not specify the names of domains that this machine is backup
              MX host for. See STANDARD_CONFIGURATION_README for how to set up
              backup MX hosts.

             By  default, the Postfix SMTP server rejects mail for recipients
              not listed with the  local_recipient_maps  parameter.   See  the
              postconf(5) manual for a description of the local_recipient_maps
              and unknown_local_recipient_reject_code parameters.

       Specify a list of host or domain names,  "/file/name"  or  "type:table"
       patterns, separated by commas and/or whitespace. A "/file/name" pattern
       is replaced by its contents; a "type:table"  lookup  table  is  matched
       when  a name matches a lookup key (the lookup result is ignored).  Con-
       tinue long lines by starting the next line with whitespace.

       Examples:

       mydestination = $myhostname, localhost.$mydomain $mydomain
       mydestination = $myhostname, localhost.$mydomain www.$mydomain, ftp.$mydomain

mydomain (default: see postconf -d output)
       The internet domain name of this mail system.  The default  is  to  use
       $myhostname  minus  the  first component, or "localdomain" (Postfix 2.3
       and later).  $mydomain is used as a default value for many  other  con-
       figuration parameters.

       Example:

       mydomain = domain.tld

myhostname (default: see postconf -d output)
       The  internet  hostname  of this mail system. The default is to use the
       fully-qualified domain name (FQDN) from gethostname(), or  to  use  the
       non-FQDN  result  from gethostname() and append ".$mydomain".  $myhost-
       name is used as a default value for many  other  configuration  parame-
       ters.

       Example:

       myhostname = host.example.com

mynetworks (default: see postconf -d output)
       The  list  of  "trusted"  remote SMTP clients that have more privileges
       than "strangers".

       In particular, "trusted" SMTP clients are allowed to relay mail through
       Postfix.  See the smtpd_relay_restrictions parameter description in the
       postconf(5) manual.

       You can specify the list of "trusted" network addresses by hand or  you
       can let Postfix do it for you (which is the default).  See the descrip-
       tion of the mynetworks_style parameter for more information.

       If you specify the mynetworks list by hand, Postfix ignores the  mynet-
       works_style setting.

       Specify  a list of network addresses or network/netmask patterns, sepa-
       rated by commas and/or whitespace. Continue long lines by starting  the
       next line with whitespace.

       The  netmask specifies the number of bits in the network part of a host
       address.  You can also specify "/file/name" or  "type:table"  patterns.
       A  "/file/name"  pattern  is  replaced  by its contents; a "type:table"
       lookup table is matched when a table entry matches a lookup string (the
       lookup result is ignored).

       The  list  is  matched left to right, and the search stops on the first
       match.  Specify "!pattern" to exclude an address or network block  from
       the  list.  The form "!/file/name" is supported only in Postfix version
       2.4 and later.

       Note 1: Pattern matching of  domain  names  is  controlled  by  the  or
       absence of "mynetworks" in the parent_domain_matches_subdomains parame-
       ter value.

       Note 2: IP version 6 address information must be specified inside [] in
       the  mynetworks  value,  and  in files specified with "/file/name".  IP
       version 6 addresses contain the ":" character, and would  otherwise  be
       confused with a "type:table" pattern.

       Examples:

       mynetworks = 127.0.0.0/8 168.100.189.0/28
       mynetworks = !192.168.0.1, 192.168.0.0/28
       mynetworks = 127.0.0.0/8 168.100.189.0/28 [::1]/128 [2001:240:587::]/64
       mynetworks = $config_directory/mynetworks
       mynetworks = hash:/etc/postfix/network_table

mynetworks_style (default: Postfix >= 3.0: host, Postfix < 3.0: subnet)
       The  method to generate the default value for the mynetworks parameter.
       This is the list of trusted networks for relay access control etc.

             Specify "mynetworks_style = host" when  Postfix  should  "trust"
              only the local machine.

             Specify  "mynetworks_style = subnet" when Postfix should "trust"
              remote SMTP clients in the same  IP  subnetworks  as  the  local
              machine.   On  Linux,  this works correctly only with interfaces
              specified with the "ifconfig" command.

             Specify "mynetworks_style = class" when Postfix  should  "trust"
              remote  SMTP  clients in the same IP class A/B/C networks as the
              local machine.  Caution: this may cause Postfix to "trust"  your
              entire  provider's network.  Instead, specify an explicit mynet-
              works list by hand, as described with the mynetworks  configura-
              tion parameter.

myorigin (default: $myhostname)
       The domain name that locally-posted mail appears to come from, and that
       locally posted mail is delivered to. The default, $myhostname, is  ade-
       quate for small sites.  If you run a domain with multiple machines, you
       should (1) change this to $mydomain and (2) set up a domain-wide  alias
       database that aliases each user to user@that.users.mailhost.

       Example:

       myorigin = $mydomain

nested_header_checks (default: $header_checks)
       Optional lookup tables for content inspection of non-MIME message head-
       ers in attached messages, as described in the  header_checks(5)  manual
       page.

       This feature is available in Postfix 2.0 and later.

newaliases_path (default: see postconf -d output)
       Sendmail  compatibility  feature  that  specifies  the  location of the
       newaliases(1) command. This command can be used to rebuild the local(8)
       aliases(5) database.

non_fqdn_reject_code (default: 504)
       The  numerical  Postfix SMTP server reply code when a client request is
       rejected by the  reject_non_fqdn_helo_hostname,  reject_non_fqdn_sender
       or reject_non_fqdn_recipient restriction.

non_smtpd_milters (default: empty)
       A  list of Milter (mail filter) applications for new mail that does not
       arrive via the Postfix smtpd(8) server. This includes local  submission
       via the sendmail(1) command line, new mail that arrives via the Postfix
       qmqpd(8) server, and old mail that is re-injected into the  queue  with
       "postsuper  -r".   Specify  space  or  comma as separator. See the MIL-
       TER_README document for details.

       This feature is available in Postfix 2.3 and later.

notify_classes (default: resource, software)
       The list of error classes that are  reported  to  the  postmaster.  The
       default  is  to report only the most serious problems. The paranoid may
       wish to turn on the policy (UCE and mail relaying) and  protocol  error
       (broken mail software) reports.

       NOTE:  postmaster  notifications  may  contain confidential information
       such as SASL passwords or message content.  It is the  system  adminis-
       trator's responsibility to treat such information with care.

       The error classes are:

       bounce (also implies 2bounce)
              Send  the  postmaster copies of the headers of bounced mail, and
              send transcripts of SMTP sessions when Postfix rejects mail. The
              notification   is   sent  to  the  address  specified  with  the
              bounce_notice_recipient configuration parameter (default:  post-
              master).

       2bounce
              Send undeliverable bounced mail to the postmaster. The notifica-
              tion   is   sent   to   the   address   specified    with    the
              2bounce_notice_recipient configuration parameter (default: post-
              master).

       data   Send the postmaster a transcript of the  SMTP  session  with  an
              error  because a critical data file was unavailable. The notifi-
              cation   is   sent   to   the   address   specified   with   the
              error_notice_recipient  configuration  parameter (default: post-
              master).
              This feature is available in Postfix 2.9 and later.

       delay  Send the postmaster copies of the headers of delayed  mail  (see
              delay_warning_time).  The  notification  is  sent to the address
              specified with the delay_notice_recipient configuration  parame-
              ter (default: postmaster).

       policy Send  the  postmaster  a  transcript  of the SMTP session when a
              client request was rejected because of (UCE) policy. The notifi-
              cation   is   sent   to   the   address   specified   with   the
              error_notice_recipient configuration parameter  (default:  post-
              master).

       protocol
              Send  the postmaster a transcript of the SMTP session in case of
              client or server protocol errors. The notification  is  sent  to
              the address specified with the error_notice_recipient configura-
              tion parameter (default: postmaster).

       resource
              Inform the postmaster of mail  not  delivered  due  to  resource
              problems.   The  notification  is  sent to the address specified
              with   the   error_notice_recipient   configuration    parameter
              (default: postmaster).

       software
              Inform  the  postmaster  of  mail  not delivered due to software
              problems.  The notification is sent  to  the  address  specified
              with    the   error_notice_recipient   configuration   parameter
              (default: postmaster).

       Examples:

       notify_classes = bounce, delay, policy, protocol, resource, software
       notify_classes = 2bounce, resource, software

nullmx_reject_code (default: 556)
       The numerical reply code when the Postfix SMTP server rejects a  sender
       or  recipient address because its domain has a nullmx DNS record (an MX
       record with an empty hostname). This is one  of  the  possible  replies
       from      the     restrictions     reject_unknown_sender_domain     and
       reject_unknown_recipient_domain.

       This feature is available in Postfix 3.0 and later.

openssl_path (default: openssl)
       The location of the OpenSSL command line program openssl(1).   This  is
       used  by  the "postfix tls" command to create private keys, certificate
       signing requests, self-signed certificates, and to compute  public  key
       digests  for  DANE  TLSA records.  In multi-instance environments, this
       parameter is always determined from the configuration  of  the  default
       Postfix instance.

       Example:

           /etc/postfix/main.cf:
               # NetBSD pkgsrc:
               openssl_path = /usr/pkg/bin/openssl
               # Local build:
               openssl_path = /usr/local/bin/openssl

       This feature is available in Postfix 3.1 and later.

owner_request_special (default: yes)
       Give  special  treatment to owner-listname and listname-request address
       localparts: don't split such addresses when the recipient_delimiter  is
       set to "-".  This feature is useful for mailing lists.

parent_domain_matches_subdomains (default: see postconf -d output)
       A list of Postfix features where the pattern "example.com" also matches
       subdomains of example.com, instead of  requiring  an  explicit  ".exam-
       ple.com"  pattern.   This  is planned backwards compatibility:  eventu-
       ally, all Postfix features are expected  to  require  explicit  ".exam-
       ple.com" style patterns when you really want to match subdomains.

       The following Postfix feature names are supported.

       Postfix version 1.0 and later
              debug_peer_list,     fast_flush_domains,     mynetworks,    per-
              mit_mx_backup_networks, relay_domains, transport_maps

       Postfix version 1.1 and later
              qmqpd_authorized_clients, smtpd_access_maps,

       Postfix version 2.8 and later
              postscreen_access_list

       Postfix version 3.0 and later
              smtpd_client_event_limit_exceptions

permit_mx_backup_networks (default: empty)
       Restrict the use of the permit_mx_backup SMTP access  feature  to  only
       domains  whose primary MX hosts match the listed networks.  The parame-
       ter value syntax is the same as with the  mynetworks  parameter;  note,
       however, that the default value is empty.

       Pattern  matching  of  domain  names  is  controlled by the presence or
       absence     of     "permit_mx_backup_networks"     in     the      par-
       ent_domain_matches_subdomains parameter value.

pickup_service_name (default: pickup)
       The  name  of  the  pickup(8) service. This service picks up local mail
       submissions from the Postfix maildrop queue.

       This feature is available in Postfix 2.0 and later.

pipe_delivery_status_filter (default: $default_delivery_status_filter)
       Optional filter for the pipe(8) delivery agent to change  the  delivery
       status  code or explanatory text of successful or unsuccessful deliver-
       ies.  See default_delivery_status_filter for details.

       This feature is available in Postfix 3.0 and later.

plaintext_reject_code (default: 450)
       The numerical Postfix SMTP server  response  code  when  a  request  is
       rejected by the reject_plaintext_session restriction.

       This feature is available in Postfix 2.3 and later.

postmulti_control_commands (default: reload flush)
       The  postfix(1)  commands that the postmulti(1) instance manager treats
       as "control" commands, that operate on  running  instances.  For  these
       commands, disabled instances are skipped.

       This feature is available in Postfix 2.6 and later.

postmulti_start_commands (default: start)
       The  postfix(1)  commands that the postmulti(1) instance manager treats
       as  "start"  commands.  For  these  commands,  disabled  instances  are
       "checked"  rather  than  "started",  and  failure  to  "start" a member
       instance of  an  instance  group  will  abort  the  start-up  of  later
       instances.

       This feature is available in Postfix 2.6 and later.

postmulti_stop_commands (default: see postconf -d output)
       The  postfix(1)  commands that the postmulti(1) instance manager treats
       as "stop" commands. For these commands, disabled instances are skipped,
       and enabled instances are processed in reverse order.

       This feature is available in Postfix 2.6 and later.

postscreen_access_list (default: permit_mynetworks)
       Permanent   white/blacklist   for  remote  SMTP  client  IP  addresses.
       postscreen(8) searches this list immediately after a remote SMTP client
       connects.   Specify  a  comma- or whitespace-separated list of commands
       (in upper or lower case) or lookup tables. The search  stops  upon  the
       first command that fires for the client IP address.

        permit_mynetworks
              Whitelist  the  client and terminate the search if the client IP
              address matches $mynetworks.  Do not subject the client  to  any
              before/after  220  greeting  tests.  Pass the connection immedi-
              ately to a Postfix SMTP server process.
              Pattern matching of domain names is controlled by  the  presence
              or    absence    of   "postscreen_access_list"   in   the   par-
              ent_domain_matches_subdomains parameter value.

        type:table
              Query the specified lookup table. Each table lookup result is an
              access  list,  except  that  access  lists inside a table cannot
              specify type:table entries.
              To discourage the use of hash, btree, etc. tables, there  is  no
              support  for  substring  matching like smtpd(8). Use CIDR tables
              instead.

        permit
              Whitelist the client and terminate the search.  Do  not  subject
              the client to any before/after 220 greeting tests. Pass the con-
              nection immediately to a Postfix SMTP server process.

        reject
              Blacklist the client  and  terminate  the  search.  Subject  the
              client  to  the  action  configured  with  the postscreen_black-
              list_action configuration parameter.

        dunno All postscreen(8) access lists implicitly have this  command  at
              the end.
              When   dunno  is executed inside a lookup table, return from the
              lookup table and evaluate the next command.
              When  dunno  is executed outside a lookup table,  terminate  the
              search,  and  subject  the client to the configured before/after
              220 greeting tests.

       Example:

       /etc/postfix/main.cf:
           postscreen_access_list = permit_mynetworks,
                       cidr:/etc/postfix/postscreen_access.cidr
           postscreen_blacklist_action = enforce

       /etc/postfix/postscreen_access.cidr:
           # Rules are evaluated in the order as specified.
           # Blacklist 192.168.* except 192.168.0.1.
           192.168.0.1         dunno
           192.168.0.0/16      reject

       This feature is available in Postfix 2.8.

postscreen_bare_newline_action (default: ignore)
       The action that postscreen(8) takes when a remote SMTP client  sends  a
       bare  newline  character,  that  is, a newline not preceded by carriage
       return.  Specify one of the following:

       ignore Ignore the failure of this test. Allow other tests to  complete.
              Do  not  repeat this test before some the result from some other
              test expires.  This option is useful for testing and  collecting
              statistics without blocking mail permanently.

       enforce
              Allow  other  tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient  infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_enable (default: no)
       Enable "bare newline" SMTP protocol tests in the postscreen(8)  server.
       These  tests  are expensive: a remote SMTP client must disconnect after
       it passes the test, before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_bare_newline_ttl (default: 30d)
       The amount of time that postscreen(8) will use the result from  a  suc-
       cessful "bare newline" SMTP protocol test. During this time, the client
       IP address is excluded from this test. The default is  long  because  a
       remote  SMTP client must disconnect after it passes the test, before it
       can talk to a real Postfix SMTP server.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter  suffix  that specifies the time unit).  Time units: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_blacklist_action (default: ignore)
       The action that postscreen(8) takes when a remote SMTP client is perma-
       nently  blacklisted with the postscreen_access_list parameter.  Specify
       one of the following:

       ignore (default)
              Ignore  this result. Allow other tests to complete.  Repeat this
              test  the  next time the client connects.  This option is useful
              for testing and collecting statistics without blocking mail.

       enforce
              Allow other tests to complete. Reject attempts to  deliver  mail
              with  a 550 SMTP reply, and log the helo/sender/recipient infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop the connection immediately with a 521  SMTP  reply.  Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_cache_cleanup_interval (default: 12h)
       The  amount  of  time  between postscreen(8) cache cleanup runs.  Cache
       cleanup increases the load on the cache database and  should  therefore
       not  be  run  frequently. This feature requires that the cache database
       supports the "delete" and "sequence" operators.  Specify a zero  inter-
       val to disable cache cleanup.

       After  each cache cleanup run, the postscreen(8) daemon logs the number
       of entries that were retained and dropped. A cleanup run is  logged  as
       "partial"  when  the  daemon  terminates  early after "postfix reload",
       "postfix stop", or no requests for $max_idle seconds.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_cache_map (default: btree:$data_directory/postscreen_cache)
       Persistent storage for the postscreen(8) server decisions.

       To  share  a  postscreen(8)  cache   between   multiple   postscreen(8)
       instances,   use  "postscreen_cache_map  =  proxy:btree:/path/to/file".
       This requires Postfix version 2.9 or later; earlier proxymap(8)  imple-
       mentations don't support cache cleanup. For an alternative approach see
       the memcache_table(5) manpage.

       This feature is available in Postfix 2.8.

postscreen_cache_retention_time (default: 7d)
       The amount of time that postscreen(8) will cache an  expired  temporary
       whitelist  entry before it is removed. This prevents clients from being
       logged as "NEW" just because their cache entry expired an hour ago.  It
       also  prevents  the cache from filling up with clients that passed some
       deep protocol test once and never came back.

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_client_connection_count_limit    (default:    $smtpd_client_connec-
       tion_count_limit)
       How  many simultaneous connections any remote SMTP client is allowed to
       have with the postscreen(8) daemon. By default, this limit is the  same
       as  with the Postfix SMTP server. Note that the triage process can take
       several seconds, with the time spent  in  postscreen_greet_wait  delay,
       and  with  the  time  spent talking to the postscreen(8) built-in dummy
       SMTP protocol engine.

       This feature is available in Postfix 2.8.

postscreen_command_count_limit (default: 20)
       The limit on  the  total  number  of  commands  per  SMTP  session  for
       postscreen(8)'s built-in SMTP protocol engine.  This SMTP engine defers
       or rejects all attempts to deliver mail, therefore there is no need  to
       enforce  separate  limits on the number of junk commands and error com-
       mands.

       This feature is available in Postfix 2.8.

postscreen_command_filter (default: $smtpd_command_filter)
       A mechanism to  transform  commands  from  remote  SMTP  clients.   See
       smtpd_command_filter for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_command_time_limit (default: normal: 300s, overload: 10s)
       The  time  limit  to  read  an entire command line with postscreen(8)'s
       built-in SMTP protocol engine.

       This feature is available in Postfix 2.8.

postscreen_disable_vrfy_command (default: $disable_vrfy_command)
       Disable the SMTP VRFY command in the postscreen(8)  daemon.   See  dis-
       able_vrfy_command for details.

       This feature is available in Postfix 2.8.

postscreen_discard_ehlo_keyword_address_maps       (default:       $smtpd_dis-
       card_ehlo_keyword_address_maps)
       Lookup tables, indexed by the remote SMTP  client  address,  with  case
       insensitive  lists  of EHLO keywords (pipelining, starttls, auth, etc.)
       that the postscreen(8) server will not send in the EHLO response  to  a
       remote  SMTP  client. See smtpd_discard_ehlo_keywords for details.  The
       table is not searched by hostname for robustness reasons.

       This feature is available in Postfix 2.8 and later.

postscreen_discard_ehlo_keywords (default: $smtpd_discard_ehlo_keywords)
       A case insensitive list of EHLO keywords (pipelining,  starttls,  auth,
       etc.)  that the postscreen(8) server will not send in the EHLO response
       to a remote SMTP client. See smtpd_discard_ehlo_keywords for details.

       This feature is available in Postfix 2.8 and later.

postscreen_dnsbl_action (default: ignore)
       The action that postscreen(8) takes when a remote  SMTP  client's  com-
       bined  DNSBL  score is equal to or greater than a threshold (as defined
       with the postscreen_dnsbl_sites and postscreen_dnsbl_threshold  parame-
       ters).  Specify one of the following:

       ignore (default)
              Ignore  the failure of this test. Allow other tests to complete.
              Repeat this test the next time the client connects.  This option
              is useful for testing and collecting statistics without blocking
              mail.

       enforce
              Allow other tests to complete. Reject attempts to  deliver  mail
              with  a 550 SMTP reply, and log the helo/sender/recipient infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop the connection immediately with a 521  SMTP  reply.  Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_max_ttl                                             (default:
       ${postscreen_dnsbl_ttl?{$postscreen_dnsbl_ttl}:{1}}h)
       The maximum amount of time that postscreen(8) will use the result  from
       a  successful  DNS-based  reputation test before a client IP address is
       required to pass that test again. If the DNS reply specifies a  shorter
       TTL  value,  that  value  will  be used unless it would be smaller than
       postscreen_dnsbl_min_ttl.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter  suffix  that specifies the time unit).  Time units: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 3.1. The default setting is  back-
       wards-compatible with older Postfix versions.

postscreen_dnsbl_min_ttl (default: 60s)
       The  minimum amount of time that postscreen(8) will use the result from
       a successful DNS-based reputation test before a client  IP  address  is
       required  to  pass that test again. If the DNS reply specifies a larger
       TTL value, that value will be used  unless  it  would  be  larger  than
       postscreen_dnsbl_max_ttl.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).  Time units:  s  (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 3.1.

postscreen_dnsbl_reply_map (default: empty)
       A  mapping  from actual DNSBL domain name which includes a secret pass-
       word, to the DNSBL domain name that postscreen will reply with when  it
       rejects  mail.   When no mapping is found, the actual DNSBL domain will
       be used.

       For maximal stability it is best to use a file that is read into memory
       such  as  pcre:,  regexp:  or texthash: (texthash: is similar to hash:,
       except a) there is no need to run postmap(1) before  the  file  can  be
       used, and b) texthash: does not detect changes after the file is read).

       Example:

       /etc/postfix/main.cf:
           postscreen_dnsbl_reply_map = texthash:/etc/postfix/dnsbl_reply

       /etc/postfix/dnsbl_reply:
          secret.zen.spamhaus.org      zen.spamhaus.org

       This feature is available in Postfix 2.8.

postscreen_dnsbl_sites (default: empty)
       Optional list of DNS white/blacklist domains, filters and  weight  fac-
       tors.  When  the  list  is  non-empty, the dnsblog(8) daemon will query
       these domains with  the  IP  addresses  of  remote  SMTP  clients,  and
       postscreen(8)  will  update  an  SMTP  client's  DNSBL  score with each
       non-error reply.

       Caution: when postscreen rejects mail, it replies with the DNSBL domain
       name.  Use  the  postscreen_dnsbl_reply_map  feature to hide "password"
       information in DNSBL domain names.

       When a client's score is equal to or greater than the threshold  speci-
       fied  with  postscreen_dnsbl_threshold, postscreen(8) can drop the con-
       nection with the remote SMTP client.

       Specify a list of domain=filter*weight entries, separated by  comma  or
       whitespace.

             When  no  "=filter"  is  specified,  postscreen(8)  will use any
              non-error DNSBL reply.  Otherwise, postscreen(8) uses only DNSBL
              replies  that match the filter. The filter has the form d.d.d.d,
              where each d is a number, or a pattern inside []  that  contains
              one or more ";"-separated numbers or number..number ranges.

             When  no  "*weight"  is  specified, postscreen(8) increments the
              remote SMTP client's DNSBL score by 1.   Otherwise,  the  weight
              must be an integral number, and postscreen(8) adds the specified
              weight to the remote SMTP client's DNSBL score.  Specify a nega-
              tive number for whitelisting.

             When  one  postscreen_dnsbl_sites  entry produces multiple DNSBL
              responses, postscreen(8) applies the weight at most once.

       Examples:

       To use example.com as a high-confidence blocklist, and  to  block  mail
       with example.net and example.org only when both agree:

       postscreen_dnsbl_threshold = 2
       postscreen_dnsbl_sites = example.com*2, example.net, example.org

       To filter only DNSBL replies containing 127.0.0.4:

       postscreen_dnsbl_sites = example.com=127.0.0.4

       This feature is available in Postfix 2.8.

postscreen_dnsbl_threshold (default: 1)
       The  inclusive  lower bound for blocking a remote SMTP client, based on
       its combined DNSBL score as  defined  with  the  postscreen_dnsbl_sites
       parameter.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_timeout (default: 10s)
       The  time  limit  for DNSBL or DNSWL lookups. This is separate from the
       timeouts  in  the  dnsblog(8)  daemon  which  are  defined  by   system
       resolver(3) routines.

       This feature is available in Postfix 3.0.

postscreen_dnsbl_ttl (default: 1h)
       The  amount  of time that postscreen(8) will use the result from a suc-
       cessful DNS-based  reputation  test  before  a  client  IP  address  is
       required to pass that test again.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).  Time units:  s  (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This  feature  is  available  in  Postfix  2.8-3.0.  It was replaced by
       postscreen_dnsbl_max_ttl in Postfix 3.1.

postscreen_dnsbl_whitelist_threshold (default: 0)
       Allow a remote SMTP client to skip "before" and  "after  220  greeting"
       protocol  tests,  based on its combined DNSBL score as defined with the
       postscreen_dnsbl_sites parameter.

       Specify a negative value to enable this feature. When a  client  passes
       the  postscreen_dnsbl_whitelist_threshold  without  having failed other
       tests, all pending or disabled tests are flagged as  completed  with  a
       time-to-live  value  equal  to  postscreen_dnsbl_ttl.   When a test was
       already completed, its time-to-live value is updated  if  it  was  less
       than postscreen_dnsbl_ttl.

       This feature is available in Postfix 2.11.

postscreen_enforce_tls (default: $smtpd_enforce_tls)
       Mandatory  TLS:  announce  STARTTLS support to remote SMTP clients, and
       require     that     clients     use     TLS      encryption.       See
       smtpd_postscreen_enforce_tls for details.

       This  feature  is  available in Postfix 2.8 and later.  Preferably, use
       postscreen_tls_security_level instead.

postscreen_expansion_filter (default: see postconf -d output)
       List of  characters  that  are  permitted  in  postscreen_reject_footer
       attribute  expansions.  See smtpd_expansion_filter for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_forbidden_commands (default: $smtpd_forbidden_commands)
       List of commands that the postscreen(8) server considers  in  violation
       of  the  SMTP  protocol.  See  smtpd_forbidden_commands for syntax, and
       postscreen_non_smtp_command_action for possible actions.

       This feature is available in Postfix 2.8.

postscreen_greet_action (default: ignore)
       The action that postscreen(8) takes when a remote  SMTP  client  speaks
       before    its    turn    within    the    time   specified   with   the
       postscreen_greet_wait parameter.  Specify one of the following:

       ignore (default)
              Ignore the failure of this test. Allow other tests to  complete.
              Repeat this test the next time the client connects.  This option
              is useful for testing and collecting statistics without blocking
              mail.

       enforce
              Allow  other  tests to complete. Reject attempts to deliver mail
              with a 550 SMTP reply, and log the helo/sender/recipient  infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop  the  connection  immediately with a 521 SMTP reply. Repeat
              this test the next time the client connects.

       In either case, postscreen(8) will not whitelist the remote SMTP client
       IP address.

       This feature is available in Postfix 2.8.

postscreen_greet_banner (default: $smtpd_banner)
       The   text   in   the   optional  "220-text..."  server  response  that
       postscreen(8) sends ahead  of  the  real  Postfix  SMTP  server's  "220
       text..."  response,  in  an attempt to confuse bad SMTP clients so that
       they speak before their turn (pre-greet).  Specify an  empty  value  to
       disable this feature.

       This feature is available in Postfix 2.8.

postscreen_greet_ttl (default: 1d)
       The  amount  of time that postscreen(8) will use the result from a suc-
       cessful PREGREET test. During this  time,  the  client  IP  address  is
       excluded  from  this  test.  The default is relatively short, because a
       good client can immediately talk to a real Postfix SMTP server.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter  suffix  that specifies the time unit).  Time units: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_greet_wait (default: normal: 6s, overload: 2s)
       The amount of time that postscreen(8) will wait for an SMTP  client  to
       send a command before its turn, and for DNS blocklist lookup results to
       arrive (default: up to 2 seconds under stress, up to 6  seconds  other-
       wise).

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).

       Time units: s (seconds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_helo_required (default: $smtpd_helo_required)
       Require that a remote SMTP client sends HELO or EHLO before  commencing
       a MAIL transaction.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_action (default: drop)
       The  action  that  postscreen(8)  takes when a remote SMTP client sends
       non-SMTP commands as specified with  the  postscreen_forbidden_commands
       parameter.  Specify one of the following:

       ignore Ignore  the failure of this test. Allow other tests to complete.
              Do not repeat this test before some the result from  some  other
              test  expires.  This option is useful for testing and collecting
              statistics without blocking mail permanently.

       enforce
              Allow other tests to complete. Reject attempts to  deliver  mail
              with  a 550 SMTP reply, and log the helo/sender/recipient infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop the connection immediately with a 521  SMTP  reply.  Repeat
              this  test the next time the client connects. This action is the
              same as with the Postfix SMTP server's  smtpd_forbidden_commands
              feature.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_enable (default: no)
       Enable  "non-SMTP  command"  tests  in  the postscreen(8) server. These
       tests are expensive: a client must disconnect after it passes the test,
       before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_non_smtp_command_ttl (default: 30d)
       The  amount  of time that postscreen(8) will use the result from a suc-
       cessful "non_smtp_command" SMTP protocol test. During  this  time,  the
       client  IP  address  is  excluded  from  this test. The default is long
       because a client must disconnect after it passes the  test,  before  it
       can talk to a real Postfix SMTP server.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).  Time units:  s  (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_pipelining_action (default: enforce)
       The  action  that  postscreen(8)  takes when a remote SMTP client sends
       multiple commands instead of sending one command and  waiting  for  the
       server to respond.  Specify one of the following:

       ignore Ignore  the failure of this test. Allow other tests to complete.
              Do not repeat this test before some the result from  some  other
              test  expires.  This option is useful for testing and collecting
              statistics without blocking mail permanently.

       enforce
              Allow other tests to complete. Reject attempts to  deliver  mail
              with  a 550 SMTP reply, and log the helo/sender/recipient infor-
              mation.  Repeat this test the next time the client connects.

       drop   Drop the connection immediately with a 521  SMTP  reply.  Repeat
              this test the next time the client connects.

       This feature is available in Postfix 2.8.

postscreen_pipelining_enable (default: no)
       Enable  "pipelining"  SMTP  protocol tests in the postscreen(8) server.
       These tests are expensive: a  good  client  must  disconnect  after  it
       passes the test, before it can talk to a real Postfix SMTP server.

       This feature is available in Postfix 2.8.

postscreen_pipelining_ttl (default: 30d)
       The  amount  of time that postscreen(8) will use the result from a suc-
       cessful "pipelining" SMTP protocol test. During this time,  the  client
       IP  address  is  excluded from this test. The default is long because a
       good client must disconnect after it passes the  test,  before  it  can
       talk to a real Postfix SMTP server.

       Specify  a  non-zero  time  value  (an  integral value plus an optional
       one-letter suffix that specifies the time unit).  Time units:  s  (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_post_queue_limit (default: $default_process_limit)
       The number of clients that can be waiting for service from a real Post-
       fix SMTP server process. When this queue  is  full,  all  clients  will
       receive a 421 response.

       This feature is available in Postfix 2.8.

postscreen_pre_queue_limit (default: $default_process_limit)
       The  number  of non-whitelisted clients that can be waiting for a deci-
       sion whether they will receive service from a real Postfix SMTP  server
       process.  When  this  queue  is  full, all non-whitelisted clients will
       receive a 421 response.

       This feature is available in Postfix 2.8.

postscreen_reject_footer (default: $smtpd_reject_footer)
       Optional information that is appended after a 4XX or 5XX  postscreen(8)
       server response. See smtpd_reject_footer for further details.

       This feature is available in Postfix 2.8 and later.

postscreen_tls_security_level (default: $smtpd_tls_security_level)
       The  SMTP  TLS  security  level  for  the  postscreen(8) server; when a
       non-empty value is specified, this overrides  the  obsolete  parameters
       postscreen_use_tls   and  postscreen_enforce_tls.  See  smtpd_tls_secu-
       rity_level for details.

       This feature is available in Postfix 2.8 and later.

postscreen_upstream_proxy_protocol (default: empty)
       The name of the proxy protocol used by  an  optional  before-postscreen
       proxy  agent.  When  a proxy agent is used, this protocol conveys local
       and    remote     address     and     port     information.     Specify
       "postscreen_upstream_proxy_protocol  =  haproxy"  to enable the haproxy
       protocol.

       This feature is available in Postfix 2.10 and later.

postscreen_upstream_proxy_timeout (default: 5s)
       The  time  limit  for   the   proxy   protocol   specified   with   the
       postscreen_upstream_proxy_protocol parameter.

       This feature is available in Postfix 2.10 and later.

postscreen_use_tls (default: $smtpd_use_tls)
       Opportunistic  TLS:  announce  STARTTLS support to remote SMTP clients,
       but do not require that clients use TLS encryption.

       This feature is available in Postfix 2.8 and  later.   Preferably,  use
       postscreen_tls_security_level instead.

postscreen_watchdog_timeout (default: 10s)
       How  much  time a postscreen(8) process may take to respond to a remote
       SMTP client command or to perform a cache operation before it is termi-
       nated  by  a  built-in watchdog timer.  This is a safety mechanism that
       prevents postscreen(8) from becoming non-responsive due  to  a  bug  in
       Postfix itself or in system software.  To avoid false alarms and unnec-
       essary cache corruption this limit cannot be set under 10s.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter  suffix  that specifies the time unit).  Time units: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_whitelist_interfaces (default: static:all)
       A  list  of  local  postscreen(8)   server   IP   addresses   where   a
       non-whitelisted remote SMTP client can obtain postscreen(8)'s temporary
       whitelist status. This status is required before the client can talk to
       a  Postfix  SMTP  server  process.   By  default,  a  client can obtain
       postscreen(8)'s whitelist status on any local postscreen(8)  server  IP
       address.

       When postscreen(8) listens on both primary and backup MX addresses, the
       postscreen_whitelist_interfaces parameter can be configured to give the
       temporary  whitelist status only when a client connects to a primary MX
       address. Once a client is whitelisted it can talk  to  a  Postfix  SMTP
       server  on  any  address.  Thus, clients that connect only to backup MX
       addresses will never become whitelisted, and will never be  allowed  to
       talk to a Postfix SMTP server process.

       Specify  a list of network addresses or network/netmask patterns, sepa-
       rated by commas and/or whitespace. The netmask specifies the number  of
       bits  in  the  network  part  of a host address. Continue long lines by
       starting the next line with whitespace.

       You  can  also  specify  "/file/name"  or  "type:table"  patterns.    A
       "/file/name" pattern is replaced by its contents; a "type:table" lookup
       table is matched when a table entry matches a lookup string (the lookup
       result is ignored).

       The  list  is  matched left to right, and the search stops on the first
       match. Specify "!pattern" to exclude an address or network  block  from
       the list.

       Note:  IP  version 6 address information must be specified inside [] in
       the postscreen_whitelist_interfaces value, and in files specified  with
       "/file/name".   IP  version  6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

       Example:

       /etc/postfix/main.cf:
           # Don't whitelist connections to the backup IP address.
           postscreen_whitelist_interfaces = !168.100.189.8, static:all

       This feature is available in Postfix 2.9 and later.

prepend_delivered_header (default: command, file, forward)
       The message delivery contexts where the Postfix local(8) delivery agent
       prepends a Delivered-To:  message header with the address that the mail
       was delivered to. This information  is  used  for  mail  delivery  loop
       detection.

       By  default,  the Postfix local delivery agent prepends a Delivered-To:
       header when forwarding mail and when delivering to file  (mailbox)  and
       command.  Turning  off the Delivered-To: header when forwarding mail is
       not recommended.

       Specify zero or more of forward, file, or command.

       Example:

       prepend_delivered_header = forward

process_id (read-only)
       The process ID of a Postfix command or daemon process.

process_id_directory (default: pid)
       The location of Postfix PID files relative to  $queue_directory.   This
       is a read-only parameter.

process_name (read-only)
       The process name of a Postfix command or daemon process.

propagate_unmatched_extensions (default: canonical, virtual)
       What  address  lookup  tables copy an address extension from the lookup
       key to the lookup result.

       For  example,  with  a  virtual(5)  mapping  of   "joe@example.com   =>
       joe.user@example.net",  the address "joe+foo@example.com" would rewrite
       to "joe.user+foo@example.net".

       Specify zero or more of canonical, virtual, alias, forward, include  or
       generic.  These  cause address extension propagation with canonical(5),
       virtual(5), and aliases(5) maps, with local(8) .forward  and  :include:
       file lookups, and with smtp(8) generic maps, respectively.

       Note:  enabling this feature for types other than canonical and virtual
       is likely to cause problems when mail  is  forwarded  to  other  sites,
       especially with mail that is sent to a mailing list exploder address.

       Examples:

       propagate_unmatched_extensions = canonical, virtual, alias,
               forward, include
       propagate_unmatched_extensions = canonical, virtual

proxy_interfaces (default: empty)
       The  network interface addresses that this mail system receives mail on
       by way of a proxy or network address translation unit.

       This feature is available in Postfix 2.0 and later.

       You must specify your "outside" proxy/NAT addresses when your system is
       a  backup MX host for other domains, otherwise mail delivery loops will
       happen when the primary MX host is down.

       Example:

       proxy_interfaces = 1.2.3.4

proxy_read_maps (default: see postconf -d output)
       The lookup tables that the proxymap(8) server is allowed to access  for
       the read-only service.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma.  Table references that don't begin with proxy: are ignored.

       This feature is available in Postfix 2.0 and later.

proxy_write_maps (default: see postconf -d output)
       The lookup tables that the proxymap(8) server is allowed to access  for
       the  read-write  service.  Postfix-owned local database files should be
       stored under the Postfix-owned data_directory.  Table  references  that
       don't begin with proxy: are ignored.

       This feature is available in Postfix 2.5 and later.

proxymap_service_name (default: proxymap)
       The  name of the proxymap read-only table lookup service.  This service
       is normally implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

proxywrite_service_name (default: proxywrite)
       The name of the proxywrite read-write table lookup service.  This  ser-
       vice is normally implemented by the proxymap(8) daemon.

       This feature is available in Postfix 2.6 and later.

qmgr_clog_warn_time (default: 300s)
       The minimal delay between warnings that a specific destination is clog-
       ging up the Postfix active queue. Specify 0 to disable.

       This feature is enabled with the helpful_warnings parameter.

       This feature is available in Postfix 2.0 and later.

qmgr_daemon_timeout (default: 1000s)
       How much time a Postfix queue manager process  may  take  to  handle  a
       request before it is terminated by a built-in watchdog timer.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.8 and later.

qmgr_fudge_factor (default: 100)
       Obsolete feature: the percentage of delivery resources that a busy mail
       system will use up for delivery of a large mailing  list message.

       This feature exists only in the oqmgr(8) old queue manager. The current
       queue manager solves the problem in a better way.

qmgr_ipc_timeout (default: 60s)
       The time limit for the queue manager to  send  or  receive  information
       over an internal communication channel.  The purpose is to break out of
       deadlock situations. If the time limit is exceeded the software  either
       retries or aborts the operation.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.8 and later.

qmgr_message_active_limit (default: 20000)
       The maximal number of messages in the active queue.

qmgr_message_recipient_limit (default: 20000)
       The maximal number of recipients held in memory by  the  Postfix  queue
       manager,  and the maximal size of the short-term, in-memory "dead" des-
       tination status cache.

qmgr_message_recipient_minimum (default: 10)
       The minimal number of in-memory recipients for any message. This  takes
       priority  over  any  other in-memory recipient limits (i.e., the global
       qmgr_message_recipient_limit and the per transport _recipient_limit) if
       necessary. The minimum value allowed for this parameter is 1.

qmqpd_authorized_clients (default: empty)
       What  remote  QMQP  clients  are allowed to connect to the Postfix QMQP
       server port.

       By default, no client is allowed to use the service.  This  is  because
       the QMQP server will relay mail to any destination.

       Specify  a  list  of  client  patterns. A list pattern specifies a host
       name, a domain name, an internet address, or  a  network/mask  pattern,
       where  the mask specifies the number of bits in the network part.  When
       a pattern specifies a file name, its contents are substituted  for  the
       file  name; when a pattern is a "type:table" table specification, table
       lookup is used instead.

       Patterns are separated by whitespace and/or commas. In order to reverse
       the  result,  precede a pattern with an exclamation point (!). The form
       "!/file/name" is supported only in Postfix version 2.4 and later.

       Pattern matching of domain names  is  controlled  by  the  presence  or
       absence of "qmqpd_authorized_clients" in the parent_domain_matches_sub-
       domains parameter value.

       Example:

       qmqpd_authorized_clients = !192.168.0.1, 192.168.0.0/24

qmqpd_client_port_logging (default: no)
       Enable logging of the remote QMQP client port in addition to the  host-
       name and IP address. The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

qmqpd_error_delay (default: 1s)
       How  long  the Postfix QMQP server will pause before sending a negative
       reply to the remote QMQP client. The purpose is to slow  down  confused
       or malicious clients.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

qmqpd_timeout (default: 300s)
       The time limit for sending or receiving information over  the  network.
       If  a  read or write operation blocks for more than $qmqpd_timeout sec-
       onds the Postfix QMQP server gives up and disconnects.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

queue_directory (default: see postconf -d output)
       The location of the Postfix top-level queue directory. This is the root
       directory of Postfix daemon processes that run chrooted.

queue_file_attribute_count_limit (default: 100)
       The maximal number of (name=value) attributes that may be stored  in  a
       Postfix queue file. The limit is enforced by the cleanup(8) server.

       This feature is available in Postfix 2.0 and later.

queue_minfree (default: 0)
       The minimal amount of free space in bytes in the queue file system that
       is needed to receive mail.  This is currently used by the Postfix  SMTP
       server to decide if it will accept any mail at all.

       By default, the Postfix SMTP server rejects MAIL FROM commands when the
       amount of free space is less than 1.5*$message_size_limit (Postfix ver-
       sion  2.1  and  later).   To specify a higher minimum free space limit,
       specify a queue_minfree value that is at least 1.5*$message_size_limit.

       With  Postfix  versions  2.0 and earlier, a queue_minfree value of zero
       means there is no minimum required amount of free space.

queue_run_delay (default: 300s)
       The time between deferred queue scans by the queue  manager;  prior  to
       Postfix 2.4 the default value was 1000s.

       This  parameter  should  be  set  less  than or equal to $minimal_back-
       off_time. See also $maximal_backoff_time.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

queue_service_name (default: qmgr)
       The name of the qmgr(8) service. This service manages the Postfix queue
       and schedules delivery requests.

       This feature is available in Postfix 2.0 and later.

rbl_reply_maps (default: empty)
       Optional lookup tables with RBL  response  templates.  The  tables  are
       indexed  by  the  RBL domain name. By default, Postfix uses the default
       template as specified with the default_rbl_reply configuration  parame-
       ter. See there for a discussion of the syntax of RBL reply templates.

       This feature is available in Postfix 2.0 and later.

readme_directory (default: see postconf -d output)
       The  location  of Postfix README files that describe how to build, con-
       figure or operate a specific Postfix subsystem or feature.

receive_override_options (default: empty)
       Enable or disable recipient validation, built-in content filtering,  or
       address  mapping.  Typically,  these are specified in master.cf as com-
       mand-line arguments for the smtpd(8), qmqpd(8) or pickup(8) daemons.

       Specify zero or more of the following options.   The  options  override
       main.cf  settings  and are either implemented by smtpd(8), qmqpd(8), or
       pickup(8) themselves, or they are forwarded to the cleanup server.

       no_unknown_recipient_checks
              Do not try to reject  unknown  recipients  (SMTP  server  only).
              This is typically specified AFTER an external content filter.

       no_address_mappings
              Disable  canonical address mapping, virtual alias map expansion,
              address masquerading,  and  automatic  BCC  (blind  carbon-copy)
              recipients.  This is typically specified BEFORE an external con-
              tent filter.

       no_header_body_checks
              Disable header/body_checks. This is typically specified AFTER an
              external content filter.

       no_milters
              Disable  Milter  (mail  filter)  applications. This is typically
              specified AFTER an external content filter.

       Note: when the "BEFORE content filter" receive_override_options setting
       is  specified  in  the main.cf file, specify the "AFTER content filter"
       receive_override_options setting in master.cf (and vice versa).

       Examples:

       receive_override_options =
           no_unknown_recipient_checks, no_header_body_checks
       receive_override_options = no_address_mappings

       This feature is available in Postfix 2.1 and later.

recipient_bcc_maps (default: empty)
       Optional BCC (blind carbon-copy)  address  lookup  tables,  indexed  by
       recipient  address.   The  BCC  address  (multiple results are not sup-
       ported) is added when mail enters from outside of Postfix.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       The table search order is as follows:

             Look up the "user+extension@domain.tld"  address  including  the
              optional address extension.

             Look  up  the  "user@domain.tld"  address  without  the optional
              address extension.

             Look up the "user+extension" address local part when the recipi-
              ent domain equals $myorigin, $mydestination, $inet_interfaces or
              $proxy_interfaces.

             Look up the "user" address local part when the recipient  domain
              equals    $myorigin,    $mydestination,    $inet_interfaces   or
              $proxy_interfaces.

             Look up the "@domain.tld" part.

       Note: with Postfix 2.3 and later the BCC address is added as if it  was
       specified  with  NOTIFY=NONE.  The sender will not be notified when the
       BCC address is undeliverable,  as  long  as  all  down-stream  software
       implements RFC 3461.

       Note:  with  Postfix 2.2 and earlier the sender will unconditionally be
       notified when the BCC address is undeliverable.

       Note: automatic BCC recipients are produced  only  for  new  mail.   To
       avoid  mailer  loops,  automatic BCC recipients are not generated after
       Postfix forwards mail  internally,  or  after  Postfix  generates  mail
       itself.

       Example:

       recipient_bcc_maps = hash:/etc/postfix/recipient_bcc

       After a change, run "postmap /etc/postfix/recipient_bcc".

       This feature is available in Postfix 2.1 and later.

recipient_canonical_classes (default: envelope_recipient, header_recipient)
       What addresses are subject to recipient_canonical_maps address mapping.
       By default, recipient_canonical_maps  address  mapping  is  applied  to
       envelope recipient addresses, and to header recipient addresses.

       Specify one or more of: envelope_recipient, header_recipient

       This feature is available in Postfix 2.2 and later.

recipient_canonical_maps (default: empty)
       Optional  address mapping lookup tables for envelope and header recipi-
       ent addresses.  The table format and lookups are documented in  canoni-
       cal(5).

       Note: $recipient_canonical_maps is processed before $canonical_maps.

       Example:

       recipient_canonical_maps = hash:/etc/postfix/recipient_canonical

recipient_delimiter (default: empty)
       The  set of characters that can separate a user name from its extension
       (example: user+foo), or a .forward file name from its extension  (exam-
       ple:  .forward+foo).   Basically, the software tries user+foo and .for-
       ward+foo before trying user and .forward.  This  implementation  recog-
       nizes  one  delimiter  character and one extension per email address or
       .forward file name.

       When the recipient_delimiter set contains multiple characters  (Postfix
       2.11  and  later),  a user name or .forward file name is separated from
       its extension by the first character that matches the  recipient_delim-
       iter set.

       See canonical(5), local(8), relocated(5) and virtual(5) for the effects
       of recipient_delimiter on lookups in aliases, canonical,  virtual,  and
       relocated  maps,  and  see the propagate_unmatched_extensions parameter
       for propagating an extension from one email address to another.

       When used in command_execution_directory, forward_path, or luser_relay,
       ${recipient_delimiter}  is replaced with the actual recipient delimiter
       that was found in the recipient email address (Postfix 2.11 and later),
       or  it is replaced with the main.cf recipient_delimiter parameter value
       (Postfix 2.10 and earlier).

       The recipient_delimiter is not applied to  the  mailer-daemon  address,
       the  postmaster address, or the double-bounce address. With the default
       "owner_request_special = yes" setting, the recipient_delimiter is  also
       not  applied  to addresses with the special "owner-" prefix or the spe-
       cial "-request" suffix.

       Examples:

       # Handle Postfix-style extensions.
       recipient_delimiter = +

       # Handle both Postfix and qmail extensions (Postfix 2.11 and later).
       recipient_delimiter = +-

       # Use .forward for mail without address extension, and for mail with
       # an unrecognized address extension.
       forward_path = $home/.forward${recipient_delimiter}${extension},
           $home/.forward

reject_code (default: 554)
       The numerical Postfix SMTP server response  code  when  a  remote  SMTP
       client request is rejected by the "reject" restriction.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

reject_tempfail_action (default: defer_if_permit)
       The Postfix SMTP server's action when a reject-type  restriction  fails
       due to a temporary error condition. Specify "defer" to defer the remote
       SMTP client request immediately.  With  the  default  "defer_if_permit"
       action,  the Postfix SMTP server continues to look for opportunities to
       reject mail, and defers the client request only if it  would  otherwise
       be accepted.

       For  finer  control, see: unverified_recipient_tempfail_action, unveri-
       fied_sender_tempfail_action,    unknown_address_tempfail_action,    and
       unknown_helo_hostname_tempfail_action.

       This feature is available in Postfix 2.6 and later.

relay_clientcerts (default: empty)
       List of tables with remote SMTP client-certificate fingerprints or pub-
       lic key fingerprints (Postfix 2.9 and later) for which the Postfix SMTP
       server  will allow access with the permit_tls_clientcerts feature.  The
       fingerprint digest algorithm is configurable via the  smtpd_tls_finger-
       print_digest  parameter  (hard-coded  as  md5  prior to Postfix version
       2.5).

       Postfix lookup tables are in the form of (key, value) pairs.  Since  we
       only  need  the  key, the value can be chosen freely, e.g.  the name of
       the  user  or   host:   D7:04:2F:A7:0B:8C:A5:21:FA:31:77:E1:41:8A:EE:80
       lutzpc.at.home

       Example:

       relay_clientcerts = hash:/etc/postfix/relay_clientcerts

       For  more  fine-grained  control,  use  check_ccert_access to select an
       appropriate  access(5)  policy   for   each   client.    See   RESTRIC-
       TION_CLASS_README.

       Note:  Postfix  2.9.0-2.9.5  computed the public key fingerprint incor-
       rectly. To use public-key fingerprints, upgrade  to  Postfix  2.9.6  or
       later.

       This feature is available with Postfix version 2.2.

relay_destination_concurrency_limit   (default:   $default_destination_concur-
       rency_limit)
       The maximal number of parallel deliveries to the same  destination  via
       the  relay  message  delivery  transport. This limit is enforced by the
       queue manager. The message delivery transport name is the  first  field
       in the entry in the master.cf file.

       This feature is available in Postfix 2.0 and later.

relay_destination_recipient_limit    (default:    $default_destination_recipi-
       ent_limit)
       The maximal number of recipients per  message  for  the  relay  message
       delivery  transport.  This  limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in  the
       master.cf file.

       Setting  this  parameter  to  a  value  of  1  changes  the  meaning of
       relay_destination_concurrency_limit from concurrency  per  domain  into
       concurrency per recipient.

       This feature is available in Postfix 2.0 and later.

relay_domains (default: Postfix >= 3.0: empty, Postfix < 3.0: $mydestination)
       What  destination  domains  (and  subdomains  thereof) this system will
       relay mail to. For details about how the relay_domains value  is  used,
       see    the    description    of    the    permit_auth_destination   and
       reject_unauth_destination SMTP recipient restrictions.

       Domains that match $relay_domains are delivered with the  $relay_trans-
       port  mail  delivery  transport.  The  SMTP  server validates recipient
       addresses with $relay_recipient_maps and rejects  non-existent  recipi-
       ents.   See   also   the   relay   domains   address   class   in   the
       ADDRESS_CLASS_README file.

       Note: Postfix will not automatically forward mail for domains that list
       this  system  as  their  primary  or  backup  MX  host.  See  the  per-
       mit_mx_backup restriction in the postconf(5) manual page.

       Specify a list of  host  or  domain  names,  "/file/name"  patterns  or
       "type:table"  lookup  tables,  separated  by  commas and/or whitespace.
       Continue long lines by  starting  the  next  line  with  whitespace.  A
       "/file/name" pattern is replaced by its contents; a "type:table" lookup
       table is matched when a (parent) domain appears as lookup key.  Specify
       "!pattern" to exclude a domain from the list. The form "!/file/name" is
       supported only in Postfix version 2.4 and later.

       Pattern matching of domain names  is  controlled  by  the  presence  or
       absence  of  "relay_domains"  in  the  parent_domain_matches_subdomains
       parameter value.

relay_domains_reject_code (default: 554)
       The numerical Postfix SMTP server response code when a  client  request
       is rejected by the reject_unauth_destination recipient restriction.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

relay_recipient_maps (default: empty)
       Optional lookup tables with all valid addresses  in  the  domains  that
       match  $relay_domains.  Specify @domain as a wild-card for domains that
       have no valid recipient list, and become a source of backscatter  mail:
       Postfix  accepts spam for non-existent recipients and then floods inno-
       cent people with undeliverable mail.  Technically, tables  listed  with
       $relay_recipient_maps  are used as lists: Postfix needs to know only if
       a lookup string is found or not, but it does not use  the  result  from
       table lookup.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       If  this  parameter  is  non-empty,  then  the Postfix SMTP server will
       reject mail to unknown relay users. This feature is off by default.

       See also the relay domains address class  in  the  ADDRESS_CLASS_README
       file.

       Example:

       relay_recipient_maps = hash:/etc/postfix/relay_recipients

       This feature is available in Postfix 2.0 and later.

relay_transport (default: relay)
       The default mail delivery transport and next-hop destination for remote
       delivery to domains listed with $relay_domains. In order of  decreasing
       precedence,  the  nexthop  destination  is taken from $relay_transport,
       $sender_dependent_relayhost_maps, $relayhost,  or  from  the  recipient
       domain.  This information can be overruled with the transport(5) table.

       Specify a string of the form transport:nexthop, where transport is  the
       name  of  a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       See  also  the  relay domains address class in the ADDRESS_CLASS_README
       file.

       This feature is available in Postfix 2.0 and later.

relayhost (default: empty)
       The next-hop destination of non-local mail; overrides non-local domains
       in recipient addresses. This information is overruled with relay_trans-
       port,    sender_dependent_default_transport_maps,    default_transport,
       sender_dependent_relayhost_maps and with the transport(5) table.

       On  an intranet, specify the organizational domain name. If your inter-
       nal DNS uses no MX records, specify the name of  the  intranet  gateway
       host instead.

       In  the  case  of SMTP, specify a domain name, hostname, hostname:port,
       [hostname]:port, [hostaddress] or [hostaddress]:port. The  form  [host-
       name] turns off MX lookups.

       If  you're  connected  via  UUCP,  see  the UUCP_README file for useful
       information.

       Examples:

       relayhost = $mydomain
       relayhost = [gateway.example.com]
       relayhost = uucphost
       relayhost = [an.ip.add.ress]

relocated_maps (default: empty)
       Optional lookup tables  with  new  contact  information  for  users  or
       domains  that  no longer exist.  The table format and lookups are docu-
       mented in relocated(5).

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       If you use this feature, run "postmap /etc/postfix/relocated" to  build
       the  necessary  DBM  or  DB file after change, then "postfix reload" to
       make the changes visible.

       Examples:

       relocated_maps = dbm:/etc/postfix/relocated
       relocated_maps = hash:/etc/postfix/relocated

remote_header_rewrite_domain (default: empty)
       Don't rewrite message headers from remote  clients  at  all  when  this
       parameter  is  empty; otherwise, rewrite message headers and append the
       specified domain name to incomplete  addresses.   The  local_header_re-
       write_clients  parameter controls what clients Postfix considers local.

       Examples:

       The  safe  setting:  append  "domain.invalid"  to   incomplete   header
       addresses  from  remote SMTP clients, so that those addresses cannot be
       confused with local addresses.

           remote_header_rewrite_domain = domain.invalid

       The default, purist, setting: don't rewrite headers from remote clients
       at all.

           remote_header_rewrite_domain =

require_home_directory (default: no)
       Require  that  a local(8) recipient's home directory exists before mail
       delivery is attempted. By default this test is  disabled.   It  can  be
       useful for environments that import home directories to the mail server
       (IMPORTING HOME DIRECTORIES IS NOT RECOMMENDED).

reset_owner_alias (default: no)
       Reset the local(8) delivery agent's idea of the owner-alias  attribute,
       when  delivering mail to a child alias that does not have its own owner
       alias.

       This feature is available in Postfix 2.8 and later. With older  Postfix
       releases, the behavior is as if this parameter is set to "yes".

       As  documented  in aliases(5), when an alias name has a companion alias
       named owner-name, delivery errors will be reported to the  owner  alias
       instead  of  the  sender. This configuration is recommended for mailing
       lists.

       A less known property of the owner alias is that  it  also  forces  the
       local(8)  delivery agent to write local and remote addresses from alias
       expansion to a new queue file, instead of attempting to deliver mail to
       local addresses as soon as they come out of alias expansion.

       Writing local addresses from alias expansion to a new queue file allows
       for robust handling of temporary delivery errors: errors with one local
       member  have  no effect on deliveries to other members of the list.  On
       the other hand, delivery to local addresses as soon as they come out of
       alias  expansion  is  fragile: a temporary error with one local address
       from alias expansion will cause the entire alias to be expanded repeat-
       edly  until  the  error  goes away, or until the message expires in the
       queue.  In that case, a problem with one list member results in  multi-
       ple message deliveries to other list members.

       The  default  behavior  of  Postfix  2.8  and  later  is  to  keep  the
       owner-alias attribute of the parent alias, when delivering  mail  to  a
       child  alias  that  does  not  have  its  own  owner alias. Then, local
       addresses from that child alias will be written to a  new  queue  file,
       and  a  temporary error with one local address will not affect delivery
       to other mailing list members.

       Unfortunately, older Postfix releases reset the  owner-alias  attribute
       when  delivering mail to a child alias that does not have its own owner
       alias.  The local(8) delivery agent  then  attempts  to  deliver  local
       addresses as soon as they come out of child alias expansion.  If deliv-
       ery to any address from child alias expansion fails  with  a  temporary
       error  condition,  the  entire  mailing list may be expanded repeatedly
       until the mail expires in the queue, resulting in  multiple  deliveries
       of the same message to mailing list members.

resolve_dequoted_address (default: yes)
       Resolve  a  recipient  address  safely instead of correctly, by looking
       inside quotes.

       By default, the Postfix address resolver does  not  quote  the  address
       localpart  as  per  RFC  822, so that additional @ or % or !  operators
       remain visible. This behavior is safe but it is also technically incor-
       rect.

       If  you  specify  "resolve_dequoted_address  =  no",  then  the Postfix
       resolver will not know about additional @ etc. operators in the address
       localpart. This opens opportunities for obscure mail relay attacks with
       user@domain@domain addresses when Postfix provides  backup  MX  service
       for Sendmail systems.

resolve_null_domain (default: no)
       Resolve  an  address  that  ends in the "@" null domain as if the local
       hostname were specified, instead of rejecting the address as invalid.

       This feature is available in Postfix 2.1 and later.   Earlier  versions
       always resolve the null domain as the local hostname.

       The  Postfix  SMTP  server  uses this feature to reject mail from or to
       addresses that end in the "@" null domain, and from addresses that  re-
       write into a form that ends in the "@" null domain.

resolve_numeric_domain (default: no)
       Resolve  "user@ipaddress"  as  "user@[ipaddress]", instead of rejecting
       the address as invalid.

       This feature is available in Postfix 2.3 and later.

rewrite_service_name (default: rewrite)
       The name of  the  address  rewriting  service.  This  service  rewrites
       addresses  to  standard  form  and resolves them to a (delivery method,
       next-hop host, recipient) triple.

       This feature is available in Postfix 2.0 and later.

sample_directory (default: /etc/postfix)
       The name of the directory with  example  Postfix  configuration  files.
       Starting  with  Postfix  2.1,  these  files have been replaced with the
       postconf(5) manual page.

send_cyrus_sasl_authzid (default: no)
       When authenticating to a remote SMTP or LMTP server  with  the  default
       setting  "no",  send  no SASL authoriZation ID (authzid); send only the
       SASL authentiCation ID (authcid) plus the authcid's password.

       The non-default setting "yes" enables the  behavior  of  older  Postfix
       versions.   These  always send a SASL authzid that is equal to the SASL
       authcid, but this  causes  interoperability  problems  with  some  SMTP
       servers.

       This feature is available in Postfix 2.4.4 and later.

sender_based_routing (default: no)
       This  parameter  should  not  be used. It was replaced by sender_depen-
       dent_relayhost_maps in Postfix version 2.3.

sender_bcc_maps (default: empty)
       Optional BCC (blind carbon-copy)  address  lookup  tables,  indexed  by
       sender  address.   The BCC address (multiple results are not supported)
       is added when mail enters from outside of Postfix.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       The table search order is as follows:

             Look up the "user+extension@domain.tld"  address  including  the
              optional address extension.

             Look  up  the  "user@domain.tld"  address  without  the optional
              address extension.

             Look up the "user+extension" address local part when the  sender
              domain  equals  $myorigin,  $mydestination,  $inet_interfaces or
              $proxy_interfaces.

             Look up the "user" address local part  when  the  sender  domain
              equals    $myorigin,    $mydestination,    $inet_interfaces   or
              $proxy_interfaces.

             Look up the "@domain.tld" part.

       Note: with Postfix 2.3 and later the BCC address is added as if it  was
       specified  with  NOTIFY=NONE.  The sender will not be notified when the
       BCC address is undeliverable,  as  long  as  all  down-stream  software
       implements RFC 3461.

       Note: with Postfix 2.2 and earlier the sender will be notified when the
       BCC address is undeliverable.

       Note: automatic BCC recipients are produced  only  for  new  mail.   To
       avoid  mailer  loops,  automatic BCC recipients are not generated after
       Postfix forwards mail  internally,  or  after  Postfix  generates  mail
       itself.

       Example:

       sender_bcc_maps = hash:/etc/postfix/sender_bcc

       After a change, run "postmap /etc/postfix/sender_bcc".

       This feature is available in Postfix 2.1 and later.

sender_canonical_classes (default: envelope_sender, header_sender)
       What  addresses  are  subject to sender_canonical_maps address mapping.
       By default, sender_canonical_maps address mapping is applied  to  enve-
       lope sender addresses, and to header sender addresses.

       Specify one or more of: envelope_sender, header_sender

       This feature is available in Postfix 2.2 and later.

sender_canonical_maps (default: empty)
       Optional  address  mapping lookup tables for envelope and header sender
       addresses.  The table format and  lookups  are  documented  in  canoni-
       cal(5).

       Example:  you  want to rewrite the SENDER address "user@ugly.domain" to
       "user@pretty.domain", while still being able to send mail to the RECIP-
       IENT address "user@ugly.domain".

       Note: $sender_canonical_maps is processed before $canonical_maps.

       Example:

       sender_canonical_maps = hash:/etc/postfix/sender_canonical

sender_dependent_default_transport_maps (default: empty)
       A  sender-dependent override for the global default_transport parameter
       setting. The tables are searched by the  envelope  sender  address  and
       @domain.  A  lookup result of DUNNO terminates the search without over-
       riding the global default_transport parameter setting.   This  informa-
       tion is overruled with the transport(5) table.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       Note:  this overrides default_transport, not transport_maps, and there-
       fore the expected syntax is that of default_transport, not  the  syntax
       of  transport_maps.   Specifically,  this  does  not support the trans-
       port_maps syntax for  null  transport,  null  nexthop,  or  null  email
       addresses.

       For  safety  reasons, this feature does not allow $number substitutions
       in regular expression maps.

       This feature is available in Postfix 2.7 and later.

sender_dependent_relayhost_maps (default: empty)
       A sender-dependent override for the global relayhost parameter setting.
       The  tables  are searched by the envelope sender address and @domain. A
       lookup result of DUNNO terminates the  search  without  overriding  the
       global relayhost parameter setting (Postfix 2.6 and later). This infor-
       mation    is    overruled    with    relay_transport,     sender_depen-
       dent_default_transport_maps,  default_transport  and  with  the  trans-
       port(5) table.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       For safety reasons, this feature does not allow  $number  substitutions
       in regular expression maps.

       This feature is available in Postfix 2.3 and later.

sendmail_fix_line_endings (default: always)
       Controls  how  the Postfix sendmail command converts email message line
       endings from <CR><LF> into UNIX format (<LF>).

       always Always convert message lines ending in <CR><LF>. This setting is
              the default with Postfix 2.9 and later.

       strict Convert message lines ending in <CR><LF> only if the first input
              line ends in <CR><LF>. This setting is backwards-compatible with
              Postfix 2.8 and earlier.

       never  Never  convert  message  lines  ending in <CR><LF>. This setting
              exists for completeness only.

       This feature is available in Postfix 2.9 and later.

sendmail_path (default: see postconf -d output)
       A Sendmail compatibility feature that specifies  the  location  of  the
       Postfix  sendmail(1)  command.  This command can be used to submit mail
       into the Postfix queue.

service_throttle_time (default: 60s)
       How long the Postfix master(8)  waits  before  forking  a  server  that
       appears to be malfunctioning.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

setgid_group (default: postdrop)
       The group ownership of set-gid Postfix commands and  of  group-writable
       Postfix  directories.  When this parameter value is changed you need to
       re-run "postfix set-permissions" (with Postfix version 2.0 and earlier:
       "/etc/postfix/post-install set-permissions".

shlib_directory (default: see 'postconf -d' output)
       The location of Postfix dynamically-linked libraries (libpostfix-*.so),
       and the default location of  Postfix  database  plugins  (postfix-*.so)
       that  have  a  relative  pathname  in  the  dynamicmaps.cf  file.   The
       shlib_directory  parameter  defaults  to  "no"  when  Postfix   dynami-
       cally-linked  libraries  and  database  plugins are disabled at compile
       time,  otherwise  it  typically   defaults   to   /usr/lib/postfix   or
       /usr/local/lib/postfix.

       Notes:

             The directory specified with shlib_directory should contain only
              Postfix-related files. Postfix dynamically-linked libraries  and
              database  plugins  should  not be installed in a "public" system
              directory such as /usr/lib or  /usr/local/lib.  Linking  Postfix
              dynamically-linked   library  files  or  database  plugins  into
              non-Postfix  programs  is  not   supported.    Postfix   dynami-
              cally-linked  libraries  and  database plugins implement a Post-
              fix-internal API that changes without maintaining compatibility.

             You can change the shlib_directory value after Postfix is built.
              However, you may have to run ldconfig or equivalent  to  prevent
              Postfix  programs from failing because the libpostfix-*.so files
              are not found.  No ldconfig command is needed if  you  keep  the
              libpostfix-*.so  files  in the compiled-in default $shlib_direc-
              tory location.

       This feature is available in Postfix 3.0 and later.

show_user_unknown_table_name (default: yes)
       Display  the  name  of  the  recipient  table  in  the  "User  unknown"
       responses.   The  extra  detail  makes trouble shooting easier but also
       reveals information that is nobody elses business.

       This feature is available in Postfix 2.0 and later.

showq_service_name (default: showq)
       The name of the showq(8) service. This service produces mail queue sta-
       tus reports.

       This feature is available in Postfix 2.0 and later.

smtp_address_preference (default: any)
       The address type ("ipv6", "ipv4" or "any") that the Postfix SMTP client
       will try first, when a destination has IPv6  and  IPv4  addresses  with
       equal  MX preference. This feature has no effect unless the inet_proto-
       cols setting enables both IPv4 and IPv6.

       Postfix SMTP client address preference has evolved.  With  Postfix  2.8
       the default is "ipv6"; earlier implementations are hard-coded to prefer
       IPv6 over IPv4.

       Notes for mail delivery between sites that have both IPv4 and IPv6 con-
       nectivity:

             The  setting "smtp_address_preference = ipv6" is unsafe.  It can
              fail to deliver mail when there is an outage that affects  IPv6,
              while the destination is still reachable over IPv4.

             The  setting "smtp_address_preference = any" is safe. With this,
              mail will eventually be delivered even if  there  is  an  outage
              that affects IPv6 or IPv4, as long as it does not affect both.

       This feature is available in Postfix 2.8 and later.

smtp_address_verify_target (default: rcpt)
       In  the  context of email address verification, the SMTP protocol stage
       that determines whether an email address is deliverable.   Specify  one
       of  "rcpt"  or  "data".   The latter is needed with remote SMTP servers
       that reject recipients after the DATA command.  Use  transport_maps  to
       apply this feature selectively:

           /etc/postfix/main.cf:
               transport_maps = hash:/etc/postfix/transport

           /etc/postfix/transport:
               smtp-domain-that-verifies-after-data    smtp-data-target:
               lmtp-domain-that-verifies-after-data    lmtp-data-target:

           /etc/postfix/master.cf:
               smtp-data-target    unix    -    -    n    -    -    smtp
                   -o smtp_address_verify_target=data
               lmtp-data-target    unix    -    -    n    -    -    lmtp
                   -o lmtp_address_verify_target=data

       Unselective  use  of the "data" target does no harm, but will result in
       unnecessary "lost connection after DATA"  events  at  remote  SMTP/LMTP
       servers.

       This feature is available in Postfix 3.0 and later.

smtp_always_send_ehlo (default: yes)
       Always send EHLO at the start of an SMTP session.

       With  "smtp_always_send_ehlo  = no", the Postfix SMTP client sends EHLO
       only when the word "ESMTP" appears in the server greeting banner (exam-
       ple: 220 spike.porcupine.org ESMTP Postfix).

smtp_bind_address (default: empty)
       An  optional  numerical  network  address  that the Postfix SMTP client
       should bind to when making an IPv4 connection.

       This can be specified in the main.cf file for all SMTP clients,  or  it
       can be specified in the master.cf file for a specific client, for exam-
       ple:

           /etc/postfix/master.cf:
               smtp ... smtp -o smtp_bind_address=11.22.33.44

       Note 1: when inet_interfaces specifies no more than one  IPv4  address,
       and that address is a non-loopback address, it is automatically used as
       the smtp_bind_address.  This supports virtual IP hosting, but can be  a
       problem on multi-homed firewalls. See the inet_interfaces documentation
       for more detail.

       Note 2: address information may be enclosed inside [], but this form is
       not required here.

smtp_bind_address6 (default: empty)
       An  optional  numerical  network  address  that the Postfix SMTP client
       should bind to when making an IPv6 connection.

       This feature is available in Postfix 2.2 and later.

       This can be specified in the main.cf file for all SMTP clients,  or  it
       can be specified in the master.cf file for a specific client, for exam-
       ple:

           /etc/postfix/master.cf:
               smtp ... smtp -o smtp_bind_address6=1:2:3:4:5:6:7:8

       Note 1: when inet_interfaces specifies no more than one  IPv6  address,
       and that address is a non-loopback address, it is automatically used as
       the smtp_bind_address6.  This supports virtual IP hosting, but can be a
       problem on multi-homed firewalls. See the inet_interfaces documentation
       for more detail.

       Note 2: address information may be enclosed inside [], but this form is
       not recommended here.

smtp_body_checks (default: empty)
       Restricted  body_checks(5)  tables  for the Postfix SMTP client.  These
       tables are searched while mail is being delivered.  Actions that change
       the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_cname_overrides_servername (default: version dependent)
       When  the remote SMTP servername is a DNS CNAME, replace the servername
       with the result from CNAME expansion for the purpose of  logging,  SASL
       password lookup, TLS policy decisions, or TLS certificate verification.
       The value "no" hardens Postfix smtp_tls_per_site  hostname-based  poli-
       cies against false hostname information in DNS CNAME records, and makes
       SASL password file lookups more predictable. This is the  default  set-
       ting as of Postfix 2.3.

       When   DNS   CNAME  records  are  validated  with  secure  DNS  lookups
       (smtp_dns_support_level = dnssec), they are always allowed to  override
       the above servername (Postfix 2.11 and later).

       This feature is available in Postfix 2.2.9 and later.

smtp_connect_timeout (default: 30s)
       The  Postfix SMTP client time limit for completing a TCP connection, or
       zero (use the operating system built-in time limit).

       When no connection can be made within the deadline,  the  Postfix  SMTP
       client  tries the next address on the mail exchanger list. Specify 0 to
       disable the time limit (i.e. use whatever timeout is implemented by the
       operating system).

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_connection_cache_destinations (default: empty)
       Permanently enable SMTP connection caching for the  specified  destina-
       tions.   With SMTP connection caching, a connection is not closed imme-
       diately after completion of a mail transaction.  Instead,  the  connec-
       tion  is kept open for up to $smtp_connection_cache_time_limit seconds.
       This allows connections to be reused  for  other  deliveries,  and  can
       improve mail delivery performance.

       Specify  a  comma  or  white  space  separated  list of destinations or
       pseudo-destinations:

             if mail is sent  without  a  relay  host:  a  domain  name  (the
              right-hand  side  of  an  email address, without the [] around a
              numeric IP address),

             if mail is sent via a relay host: a relay host name (without  []
              or  non-default  TCP  port),  as  specified in main.cf or in the
              transport map,

             if mail is sent via a UNIX-domain socket:  a  pathname  (without
              the unix: prefix),

             a  /file/name  with  domain  names  and/or  relay  host names as
              defined above,

             a "type:table" with domain names and/or relay host names on  the
              left-hand  side.   The  right-hand side result from "type:table"
              lookups is ignored.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_on_demand (default: yes)
       Temporarily enable SMTP connection caching while a  destination  has  a
       high volume of mail in the active queue.  With SMTP connection caching,
       a connection is not closed  immediately  after  completion  of  a  mail
       transaction.  Instead, the connection is kept open for up to $smtp_con-
       nection_cache_time_limit seconds.  This allows connections to be reused
       for other deliveries, and can improve mail delivery performance.

       This feature is available in Postfix 2.2 and later.

smtp_connection_cache_time_limit (default: 2s)
       When  SMTP  connection  caching  is enabled, the amount of time that an
       unused SMTP client socket is kept open before it  is  closed.   Do  not
       specify larger values without permission from the remote sites.

       This feature is available in Postfix 2.2 and later.

smtp_connection_reuse_count_limit (default: 0)
       When  SMTP  connection  caching is enabled, the number of times that an
       SMTP session may be reused before it is closed,  or  zero  (no  limit).
       With a reuse count limit of N, a connection is used up to N+1 times.

       NOTE: This feature is unsafe. When a high-volume destination has multi-
       ple inbound MTAs, then the slowest inbound MTA will  attract  the  most
       connections  to  that destination.  This limitation does not exist with
       the smtp_connection_reuse_time_limit feature.

       This feature is available in Postfix 2.11.

smtp_connection_reuse_time_limit (default: 300s)
       The amount of time during which Postfix will  use  an  SMTP  connection
       repeatedly.  The timer starts when the connection is initiated (i.e. it
       includes the connect, greeting and helo latency,  in  addition  to  the
       latencies of subsequent mail delivery transactions).

       This feature addresses a performance stability problem with remote SMTP
       servers. This problem is not specific to Postfix: it  can  happen  when
       any  MTA  sends large amounts of SMTP email to a site that has multiple
       MX hosts.

       The problem starts when one of a set of MX hosts  becomes  slower  than
       the  rest.   Even though SMTP clients connect to fast and slow MX hosts
       with equal probability, the slow MX host ends up with more simultaneous
       inbound  connections than the faster MX hosts, because the slow MX host
       needs more time to serve each client request.

       The slow MX host becomes  a  connection  attractor.   If  one  MX  host
       becomes  N  times  slower  than  the  rest,  it dominates mail delivery
       latency unless there are more than N  fast  MX  hosts  to  counter  the
       effect.  And  if  the  number  of  MX hosts is smaller than N, the mail
       delivery latency becomes  effectively  that  of  the  slowest  MX  host
       divided by the total number of MX hosts.

       The solution uses connection caching in a way that differs from Postfix
       version 2.2.  By limiting the amount of time during which a  connection
       can  be  used  repeatedly (instead of limiting the number of deliveries
       over that connection), Postfix not only restores fairness in  the  dis-
       tribution of simultaneous connections across a set of MX hosts, it also
       favors deliveries over connections that perform well, which is  exactly
       what we want.

       The  default  reuse time limit, 300s, is comparable to the various smtp
       transaction timeouts which are fair estimates of maximum excess latency
       for  a slow delivery.  Note that hosts may accept thousands of messages
       over a single connection  within  the  default  connection  reuse  time
       limit.  This number is much larger than the default Postfix version 2.2
       limit of 10 messages per cached connection. It may prove  necessary  to
       lower the limit to avoid interoperability issues with MTAs that exhibit
       bugs when many messages are delivered via a single connection.  A lower
       reuse  time limit risks losing the benefit of connection reuse when the
       average connection and mail delivery latency  exceeds  the  reuse  time
       limit.

       This feature is available in Postfix 2.3 and later.

smtp_data_done_timeout (default: 600s)
       The  Postfix  SMTP  client time limit for sending the SMTP ".", and for
       receiving the remote SMTP server response.

       When no response is received within the deadline, a warning  is  logged
       that the mail may be delivered multiple times.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_data_init_timeout (default: 120s)
       The Postfix SMTP client time limit for sending the SMTP  DATA  command,
       and for receiving the remote SMTP server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_data_xfer_timeout (default: 180s)
       The Postfix SMTP client time limit for sending the  SMTP  message  con-
       tent.    When   the   connection   makes  no  progress  for  more  than
       $smtp_data_xfer_timeout seconds the Postfix SMTP client terminates  the
       transfer.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_defer_if_no_mx_address_found (default: no)
       Defer mail delivery when no MX record resolves to an IP address.

       The default (no) is to return the mail  as  undeliverable.  With  older
       Postfix  versions  the  default  was to keep trying to deliver the mail
       until someone fixed the MX record or until the mail was too old.

       Note: the Postfix SMTP client always ignores MX records with  equal  or
       worse preference than the local MTA itself.

       This feature is available in Postfix 2.1 and later.

smtp_delivery_status_filter (default: $default_delivery_status_filter)
       Optional  filter  for the smtp(8) delivery agent to change the delivery
       status code or explanatory text of successful or unsuccessful  deliver-
       ies.  See default_delivery_status_filter for details.

       NOTE: This feature modifies Postfix SMTP client error or non-error mes-
       sages that may or may not be derived from remote SMTP server responses.
       In  contrast, the smtp_reply_filter feature modifies remote SMTP server
       responses only.

smtp_destination_concurrency_limit   (default:    $default_destination_concur-
       rency_limit)
       The  maximal  number of parallel deliveries to the same destination via
       the smtp message delivery transport. This  limit  is  enforced  by  the
       queue  manager.  The message delivery transport name is the first field
       in the entry in the master.cf file.

smtp_destination_recipient_limit    (default:     $default_destination_recipi-
       ent_limit)
       The  maximal  number  of  recipients  per  message for the smtp message
       delivery transport. This limit is enforced by the  queue  manager.  The
       message  delivery transport name is the first field in the entry in the
       master.cf file.

       Setting this parameter to a value of 1 changes the meaning of smtp_des-
       tination_concurrency_limit from concurrency per domain into concurrency
       per recipient.

smtp_discard_ehlo_keyword_address_maps (default: empty)
       Lookup tables, indexed by the remote SMTP  server  address,  with  case
       insensitive  lists  of EHLO keywords (pipelining, starttls, auth, etc.)
       that the Postfix SMTP client will ignore in the EHLO  response  from  a
       remote SMTP server. See smtp_discard_ehlo_keywords for details. The ta-
       ble  is  not  indexed  by  hostname  for  consistency  with  smtpd_dis-
       card_ehlo_keyword_address_maps.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       This feature is available in Postfix 2.2 and later.

smtp_discard_ehlo_keywords (default: empty)
       A  case  insensitive list of EHLO keywords (pipelining, starttls, auth,
       etc.) that the Postfix SMTP client will ignore  in  the  EHLO  response
       from a remote SMTP server.

       This feature is available in Postfix 2.2 and later.

       Notes:

             Specify the silent-discard pseudo keyword to prevent this action
              from being logged.

             Use the smtp_discard_ehlo_keyword_address_maps feature  to  dis-
              card EHLO keywords selectively.

smtp_dns_reply_filter (default: empty)
       Optional  filter  for  Postfix SMTP client DNS lookup results.  Specify
       zero or more lookup tables.  The lookup  tables  are  searched  in  the
       given  order  for  a match with the DNS lookup result, converted to the
       following form:

           name ttl class type preference value

       The class field is always "IN", the preference field exists only for MX
       records, the names of hosts, domains, etc.  end in ".", and those names
       are in ASCII form (xn--mumble form in the case of UTF8 names).

       When a match is found, the table lookup result specifies an action.  By
       default,  the  table  query  and  the action name are case-insensitive.
       Currently, only the IGNORE action is implemented.

       Notes:

             Postfix DNS reply filters have no effect on implicit DNS lookups
              through nsswitch.conf or equivalent mechanisms.

             The  Postfix  SMTP/LMTP  client  uses  smtp_dns_reply_filter and
              lmtp_dns_reply_filter only to discover a  remote  SMTP  or  LMTP
              service  (record  types  MX, A, AAAAA, and TLSA).  These lookups
              are also made to implement the features reject_unverified_sender
              and reject_unverified_recipient.

             The  Postfix SMTP/LMTP client defers mail delivery when a filter
              removes all lookup results from a successful query.

             Postfix SMTP server uses smtpd_dns_reply_filter only to look  up
              MX,  A,  AAAAA,  and  TXT  records  to  implement  the  features
              reject_unknown_helo_hostname,      reject_unknown_sender_domain,
              reject_unknown_recipient_domain,        reject_rbl_*,        and
              reject_rhsbl_*.

             The Postfix SMTP server logs a warning or defers  mail  delivery
              when  a  filter  removes  all  lookup  results from a successful
              query.

       Example: ignore Google AAAA records in Postfix SMTP client DNS lookups,
       because Google sometimes hard-rejects mail from IPv6 clients with valid
       PTR etc. records.

       /etc/postfix/main.cf:
           smtp_dns_reply_filter = pcre:/etc/postfix/smtp_dns_reply_filter

       /etc/postfix/smtp_dns_reply_filter:
           # /domain ttl IN AAAA address/ action, all case-insensitive.
           # Note: the domain name ends in ".".
           /^\S+\.google\.com\.\s+\S+\s+\S+\s+AAAA\s+/ IGNORE

       This feature is available in Postfix 3.0 and later.

smtp_dns_resolver_options (default: empty)
       DNS Resolver options for the Postfix SMTP client.  Specify zero or more
       of  the  following  options,  separated by comma or whitespace.  Option
       names are case-sensitive. Some options refer to domain names  that  are
       specified in the file /etc/resolv.conf or equivalent.

       res_defnames
              Append  the current domain name to single-component names (those
              that do not contain a "." character). This can produce incorrect
              results, and is the hard-coded behavior prior to Postfix 2.8.

       res_dnsrch
              Search  for  host  names  in  the  current  domain and in parent
              domains. This can produce incorrect results and is therefore not
              recommended.

       This feature is available in Postfix 2.8 and later.

smtp_dns_support_level (default: empty)
       Level  of  DNS support in the Postfix SMTP client.  With "smtp_dns_sup-
       port_level"  left  at  its  empty  default  value,  the  legacy   "dis-
       able_dns_lookups"  parameter  controls  whether  DNS  is enabled in the
       Postfix SMTP client, otherwise the legacy parameter is ignored.

       Specify one of the following:

       disabled
              Disable DNS lookups.  No MX lookups are performed  and  hostname
              to  address  lookups are unconditionally "native".  This setting
              is not appropriate for hosts that deliver  mail  to  the  public
              Internet.   Some  obsolete  how-to documents recommend disabling
              DNS lookups in some configurations with  content_filters.   This
              is no longer required and strongly discouraged.

       enabled
              Enable DNS lookups.  Nexthop destination domains not enclosed in
              "[]" will be subject to MX lookups.  If "dns" and  "native"  are
              included  in the "smtp_host_lookup" parameter value, DNS will be
              queried first to resolve MX-host A records, followed by "native"
              lookups if no answer is found in DNS.

       dnssec Enable  DNSSEC  lookups.   The "dnssec" setting differs from the
              "enabled" setting above in the following ways:

             Any MX lookups will  set  RES_USE_DNSSEC  and  RES_USE_EDNS0  to
              request  DNSSEC-validated  responses.  If  the  MX  response  is
              DNSSEC-validated the corresponding hostnames are considered val-
              idated.

             The  address  lookups of validated hostnames are also validated,
              (provided  of  course  "smtp_host_lookup"  includes  "dns",  see
              below).

             Temporary failures in DNSSEC-enabled hostname-to-address resolu-
              tion block any "native" lookups.   Additional  "native"  lookups
              only  happen when DNSSEC lookups hard-fail (NODATA or NXDOMAIN).

       The  Postfix  SMTP  client  considers  non-MX  "[nexthop]"  and  "[nex-
       thop]:port"  destinations equivalent to statically-validated MX records
       of the form "nexthop.  IN MX 0 nexthop."  Therefore, with "dnssec" sup-
       port turned on, validated hostname-to-address lookups apply to the nex-
       thop domain of any "[nexthop]" or "[nexthop]:port"  destination.   This
       is also true for LMTP "inet:host" and "inet:host:port" destinations, as
       LMTP hostnames are never subject to MX lookups.

       The "dnssec" setting is recommended only if you plan to use the dane or
       dane-only  TLS  security  level,  otherwise  enabling DNSSEC support in
       Postfix offers no additional security.  Postfix DNSSEC  support  relies
       on  an  upstream recursive nameserver that validates DNSSEC signatures.
       Such a DNS server will always filter out  forged  DNS  responses,  even
       when Postfix itself is not configured to use DNSSEC.

       When using Postfix DANE support the "smtp_host_lookup" parameter should
       include "dns", as DANE is not applicable to hosts resolved via "native"
       lookups.

       As  mentioned  above,  Postfix  is  not  a validating stub resolver; it
       relies on the system's  configured  DNSSEC-validating  recursive  name-
       server  to  perform  all  DNSSEC  validation.   Since this nameserver's
       DNSSEC-validated responses will be fully trusted, it is strongly recom-
       mended  that  the  MTA  host  have  a local DNSSEC-validating recursive
       caching nameserver listening on a loopback address, and  be  configured
       to  use  only  this nameserver for all lookups.  Otherwise, Postfix may
       remain subject to man-in-the-middle attacks that forge  responses  from
       the recursive nameserver

       DNSSEC support requires a version of Postfix compiled against a reason-
       ably-modern DNS resolver(3) library that implements the  RES_USE_DNSSEC
       and RES_USE_EDNS0 resolver options.

       This feature is available in Postfix 2.11 and later.

smtp_enforce_tls (default: no)
       Enforcement  mode: require that remote SMTP servers use TLS encryption,
       and never send mail in the clear.  This also requires that  the  remote
       SMTP  server hostname matches the information in the remote server cer-
       tificate, and that the remote SMTP server certificate was issued  by  a
       CA  that  is  trusted  by  the  Postfix SMTP client. If the certificate
       doesn't verify or the hostname doesn't match, delivery is deferred  and
       mail stays in the queue.

       The  server  hostname is matched against all names provided as dNSNames
       in the SubjectAlternativeName.  If no dNSNames are specified, the  Com-
       monName   is   checked.    The   behavior   may  be  changed  with  the
       smtp_tls_enforce_peername option.

       This option is useful only if you are definitely  sure  that  you  will
       only  connect to servers that support RFC 2487 _and_ that provide valid
       server certificates.  Typical use is for clients that  send  all  their
       email to a dedicated mailhub.

       This  feature  is  available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtp_tls_security_level instead.

smtp_fallback_relay (default: $fallback_relay)
       Optional list of relay hosts for SMTP destinations that can't be  found
       or that are unreachable. With Postfix 2.2 and earlier this parameter is
       called fallback_relay.

       By default, mail is returned to the sender when a  destination  is  not
       found, and delivery is deferred when a destination is unreachable.

       With  bulk  email  deliveries, it can be beneficial to run the fallback
       relay MTA on the same host, so that it can reuse the sender IP address.
       This  speeds up deliveries that are delayed by IP-based reputation sys-
       tems (greylist, etc.).

       The fallback relays must be SMTP destinations. Specify a domain,  host,
       host:port,  [host]:port,  [address]  or [address]:port; the form [host]
       turns off MX lookups.  If you specify multiple SMTP destinations, Post-
       fix will try them in the specified order.

       To  prevent  mailer loops between MX hosts and fall-back hosts, Postfix
       version 2.2 and later will not use the fallback relays for destinations
       that it is MX host for (assuming DNS lookup is turned on).

smtp_generic_maps (default: empty)
       Optional  lookup  tables  that perform address rewriting in the Postfix
       SMTP client, typically to transform a  locally  valid  address  into  a
       globally  valid address when sending mail across the Internet.  This is
       needed when the local machine does not have  its  own  Internet  domain
       name, but uses something like localdomain.local instead.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       The table format and lookups are documented in generic(5); examples are
       shown in the ADDRESS_REWRITING_README and STANDARD_CONFIGURATION_README
       documents.

       This feature is available in Postfix 2.2 and later.

smtp_header_checks (default: empty)
       Restricted  header_checks(5) tables for the Postfix SMTP client.  These
       tables are searched while mail is being delivered.  Actions that change
       the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_helo_name (default: $myhostname)
       The hostname to send in the SMTP HELO or EHLO command.

       The  default  value  is  the  machine  hostname.  Specify a hostname or
       [ip.add.re.ss].

       This information can be specified in the  main.cf  file  for  all  SMTP
       clients,  or  it  can be specified in the master.cf file for a specific
       client, for example:

           /etc/postfix/master.cf:
               mysmtp ... smtp -o smtp_helo_name=foo.bar.com

       This feature is available in Postfix 2.0 and later.

smtp_helo_timeout (default: 300s)
       The Postfix SMTP client time limit for sending the HELO  or  EHLO  com-
       mand, and for receiving the initial remote SMTP server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_host_lookup (default: dns)
       What mechanisms the Postfix SMTP client uses to look  up  a  host's  IP
       address.  This parameter is ignored when DNS lookups are disabled (see:
       disable_dns_lookups and smtp_dns_support_level).  The  "dns"  mechanism
       is always tried before "native" if both are listed.

       Specify one of the following:

       dns    Hosts can be found in the DNS (preferred).

       native Use the native naming service only (nsswitch.conf, or equivalent
              mechanism).

       dns, native
              Use the native service for hosts not found in the DNS.

       This feature is available in Postfix 2.1 and later.

smtp_line_length_limit (default: 998)
       The maximal length of message header and body lines that  Postfix  will
       send  via  SMTP. This limit does not include the <CR><LF> at the end of
       each line.  Longer lines are broken by inserting "<CR><LF><SPACE>",  to
       minimize the damage to MIME formatted mail.

       The  Postfix  limit of 998 characters not including <CR><LF> is consis-
       tent with the SMTP limit of 1000 characters  including  <CR><LF>.   The
       Postfix limit was 990 with Postfix 2.8 and earlier.

smtp_mail_timeout (default: 300s)
       The  Postfix  SMTP client time limit for sending the MAIL FROM command,
       and for receiving the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_mime_header_checks (default: empty)
       Restricted  mime_header_checks(5)  tables  for the Postfix SMTP client.
       These tables are searched while mail is being delivered.  Actions  that
       change the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_mx_address_limit (default: 5)
       The  maximal number of MX (mail exchanger) IP addresses that can result
       from Postfix SMTP client mail exchanger lookups, or  zero  (no  limit).
       Prior to Postfix version 2.3, this limit was disabled by default.

       This feature is available in Postfix 2.1 and later.

smtp_mx_session_limit (default: 2)
       The  maximal  number  of  SMTP sessions per delivery request before the
       Postfix SMTP client gives up or delivers to a fall-back relay host,  or
       zero  (no  limit).  This restriction ignores sessions that fail to com-
       plete the SMTP initial handshake (Postfix version 2.2 and  earlier)  or
       that  fail  to complete the EHLO and TLS handshake (Postfix version 2.3
       and later).

       This feature is available in Postfix 2.1 and later.

smtp_nested_header_checks (default: empty)
       Restricted nested_header_checks(5) tables for the Postfix SMTP  client.
       These  tables are searched while mail is being delivered.  Actions that
       change the delivery time or destination are not available.

       This feature is available in Postfix 2.5 and later.

smtp_never_send_ehlo (default: no)
       Never send EHLO  at  the  start  of  an  SMTP  session.  See  also  the
       smtp_always_send_ehlo parameter.

smtp_per_record_deadline (default: no)
       Change  the  behavior  of  the  smtp_*_timeout time limits, from a time
       limit per read or write system call, to a time limit to send or receive
       a  complete record (an SMTP command line, SMTP response line, SMTP mes-
       sage content line, or TLS protocol message).  This  limits  the  impact
       from hostile peers that trickle data one byte at a time.

       Note:  when per-record deadlines are enabled, a short timeout may cause
       problems with TLS over very slow network connections.  The reasons  are
       that  a  TLS protocol message can be up to 16 kbytes long (with TLSv1),
       and that an entire TLS protocol message must be sent or received within
       the per-record deadline.

       This  feature is available in Postfix 2.9 and later. With older Postfix
       releases, the behavior is as if this parameter is set to "no".

smtp_pix_workaround_delay_time (default: 10s)
       How long the Postfix SMTP client pauses before sending  ".<CR><LF>"  in
       order to work around the PIX firewall "<CR><LF>.<CR><LF>" bug.

       Choosing  a too short time makes this workaround ineffective when send-
       ing large messages over slow network connections.

smtp_pix_workaround_maps (default: empty)
       Lookup tables, indexed by the remote SMTP server address, with per-des-
       tination  workarounds  for  CISCO  PIX firewall bugs.  The table is not
       indexed  by  hostname  for  consistency   with   smtp_discard_ehlo_key-
       word_address_maps.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       This feature is available in Postfix 2.4 and later.

smtp_pix_workaround_threshold_time (default: 500s)
       How  long a message must be queued before the Postfix SMTP client turns
       on the PIX firewall "<CR><LF>.<CR><LF>"  bug  workaround  for  delivery
       through firewalls with "smtp fixup" mode turned on.

       By  default,  the  workaround is turned off for mail that is queued for
       less than 500 seconds. In  other  words,  the  workaround  is  normally
       turned off for the first delivery attempt.

       Specify 0 to enable the PIX firewall "<CR><LF>.<CR><LF>" bug workaround
       upon the first delivery attempt.

smtp_pix_workarounds (default: disable_esmtp, delay_dotcrlf)
       A list that specifies zero or more workarounds for CISCO  PIX  firewall
       bugs.  These  workarounds  are  implemented by the Postfix SMTP client.
       Workaround names are separated by comma or space, and are case insensi-
       tive.   This  parameter  setting  can be overruled with per-destination
       smtp_pix_workaround_maps settings.

       delay_dotcrlf
              Insert a delay before sending ".<CR><LF>" after the end  of  the
              message  content.   The  delay  is subject to the smtp_pix_work-
              around_delay_time and smtp_pix_workaround_threshold_time parame-
              ter settings.

       disable_esmtp
              Disable all extended SMTP commands: send HELO instead of EHLO.

       This  feature  is  available in Postfix 2.4 and later. The default set-
       tings are backwards compatible with earlier Postfix versions.

smtp_quit_timeout (default: 300s)
       The Postfix SMTP client time limit for sending the  QUIT  command,  and
       for receiving the remote SMTP server response.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtp_quote_rfc821_envelope (default: yes)
       Quote addresses in Postfix SMTP client MAIL FROM and RCPT  TO  commands
       as required by RFC 5321. This includes putting quotes around an address
       localpart that ends in ".".

       The default is to comply with RFC 5321. If you have to send mail  to  a
       broken SMTP server, configure a special SMTP client in master.cf:

           /etc/postfix/master.cf:
               broken-smtp . . . smtp -o smtp_quote_rfc821_envelope=no

       and  route  mail  for  the destination in question to the "broken-smtp"
       message delivery with a transport(5) table.

       This feature is available in Postfix 2.1 and later.

smtp_randomize_addresses (default: yes)
       Randomize the order of equal-preference MX host addresses.  This  is  a
       performance feature of the Postfix SMTP client.

smtp_rcpt_timeout (default: 300s)
       The  Postfix  SMTP  client time limit for sending the SMTP RCPT TO com-
       mand, and for receiving the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

smtp_reply_filter (default: empty)
       A mechanism to transform replies from remote SMTP servers one line at a
       time.  This is a last-resort tool to work around  server  replies  that
       break  interoperability  with  the  Postfix  SMTP  client.   Other uses
       involve  fault  injection  to  test  Postfix's  handling   of   invalid
       responses.

       Notes:

             In  the case of a multi-line reply, the Postfix SMTP client uses
              the final reply line's numerical SMTP reply  code  and  enhanced
              status code.

             The  numerical  SMTP  reply code (XYZ) takes precedence over the
              enhanced status code (X.Y.Z).  When  the  enhanced  status  code
              initial digit differs from the SMTP reply code initial digit, or
              when no enhanced status code is present, the Postfix SMTP client
              uses a generic enhanced status code (X.0.0) instead.

       Specify the name of a "type:table" lookup table. The search string is a
       single SMTP reply line as received from the remote SMTP server,  except
       that  the trailing <CR><LF> are removed.  When the lookup succeeds, the
       result replaces the single SMTP reply line.

       Examples:

       /etc/postfix/main.cf:
           smtp_reply_filter = pcre:/etc/postfix/reply_filter

       /etc/postfix/reply_filter:
           # Transform garbage into "250-filler..." so that it looks like
           # one line from a multi-line reply. It does not matter what we
           # substitute here as long it has the right syntax.  The Postfix
           # SMTP client will use the final line's numerical SMTP reply
           # code and enhanced status code.
           !/^([2-5][0-9][0-9]($|[- ]))/ 250-filler for garbage

       This feature is available in Postfix 2.7.

smtp_rset_timeout (default: 20s)
       The Postfix SMTP client time limit for sending the  RSET  command,  and
       for  receiving  the  remote SMTP server response. The SMTP client sends
       RSET in order to finish a recipient address probe, or to verify that  a
       cached session is still usable.

       This feature is available in Postfix 2.1 and later.

smtp_sasl_auth_cache_name (default: empty)
       An optional table to prevent repeated SASL authentication failures with
       the same remote SMTP server hostname, username and password. Each table
       (key,  value) pair contains a server name, a username and password, and
       the full server response. This information is stored when a remote SMTP
       server  rejects  an  authentication  attempt with a 535 reply code.  As
       long as the smtp_sasl_password_maps information does no change, and  as
       long  as the smtp_sasl_auth_cache_name information does not expire (see
       smtp_sasl_auth_cache_time) the Postfix SMTP client avoids SASL  authen-
       tication  attempts  with  the  same  server, username and password, and
       instead   bounces   or   defers   mail   as   controlled    with    the
       smtp_sasl_auth_soft_bounce configuration parameter.

       Use   a   per-destination  delivery  concurrency  of  1  (for  example,
       "smtp_destination_concurrency_limit  =  1",  "relay_destination_concur-
       rency_limit = 1", etc.), otherwise multiple delivery agents may experi-
       ence a login failure at the same time.

       The table must be accessed via the proxywrite  service,  i.e.  the  map
       name  must  start  with  "proxy:". The table should be stored under the
       directory specified with the data_directory parameter.

       This feature uses cryptographic hashing  to  protect  plain-text  pass-
       words, and requires that Postfix is compiled with TLS support.

       Example:

       smtp_sasl_auth_cache_name = proxy:btree:/var/db/postfix/sasl_auth_cache

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_cache_time (default: 90d)
       The  maximal  age  of  an  smtp_sasl_auth_cache_name entry before it is
       removed.

       This feature is available in Postfix 2.5 and later.

smtp_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix SMTP client.  By default, the
       Postfix SMTP client uses no authentication.

       Example:

       smtp_sasl_auth_enable = yes

smtp_sasl_auth_soft_bounce (default: yes)
       When  a remote SMTP server rejects a SASL authentication request with a
       535 reply code, defer mail delivery instead of returning mail as  unde-
       liverable.  The latter behavior was hard-coded prior to Postfix version
       2.5.

       Note: the setting "yes" overrides the global soft_bounce parameter, but
       the setting "no" does not.

       Example:

       # Default as of Postfix 2.5
       smtp_sasl_auth_soft_bounce = yes
       # The old hard-coded default
       smtp_sasl_auth_soft_bounce = no

       This feature is available in Postfix 2.5 and later.

smtp_sasl_mechanism_filter (default: empty)
       If non-empty, a Postfix SMTP client filter for the remote SMTP server's
       list of offered SASL mechanisms.  Different client and server implemen-
       tations  may support different mechanism lists; by default, the Postfix
       SMTP client will use the  intersection  of  the  two.  smtp_sasl_mecha-
       nism_filter  specifies  an  optional  third mechanism list to intersect
       with.

       Specify mechanism names, "/file/name" patterns or  "type:table"  lookup
       tables.  The  right-hand  side  result  from  "type:table"  lookups  is
       ignored. Specify "!pattern" to exclude a mechanism name from the  list.
       The  form  "!/file/name"  is  supported only in Postfix version 2.4 and
       later.

       This feature is available in Postfix 2.2 and later.

       Examples:

       smtp_sasl_mechanism_filter = plain, login
       smtp_sasl_mechanism_filter = /etc/postfix/smtp_mechs
       smtp_sasl_mechanism_filter = !gssapi, !login, static:rest

smtp_sasl_password_maps (default: empty)
       Optional Postfix SMTP client lookup tables with  one  username:password
       entry per sender, remote hostname or next-hop domain. Per-sender lookup
       is done only when sender-dependent authentication is  enabled.   If  no
       username:password entry is found, then the Postfix SMTP client will not
       attempt to authenticate to the remote host.

       The Postfix SMTP client opens the lookup table before going  to  chroot
       jail, so you can leave the password file in /etc/postfix.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

smtp_sasl_path (default: empty)
       Implementation-specific information that the Postfix SMTP client passes
       through to the  SASL  plug-in  implementation  that  is  selected  with
       smtp_sasl_type.   Typically  this specifies the name of a configuration
       file or rendezvous point.

       This feature is available in Postfix 2.3 and later.

smtp_sasl_security_options (default: noplaintext, noanonymous)
       Postfix SMTP client SASL security options; as of Postfix 2.3  the  list
       of available features depends on the SASL client implementation that is
       selected with smtp_sasl_type.

       The following security features are defined for the cyrus  client  SASL
       implementation:

       Specify zero or more of the following:

       noplaintext
              Disallow methods that use plaintext passwords.

       noactive
              Disallow methods subject to active (non-dictionary) attack.

       nodictionary
              Disallow methods subject to passive (dictionary) attack.

       noanonymous
              Disallow methods that allow anonymous authentication.

       mutual_auth
              Only  allow  methods  that  provide  mutual  authentication (not
              available with SASL version 1).

       Example:

       smtp_sasl_security_options = noplaintext

smtp_sasl_tls_security_options (default: $smtp_sasl_security_options)
       The SASL authentication security options that the Postfix  SMTP  client
       uses for TLS encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtp_sasl_tls_verified_security_options     (default:     $smtp_sasl_tls_secu-
       rity_options)
       The SASL authentication security options that the Postfix  SMTP  client
       uses  for  TLS  encrypted SMTP sessions with a verified server certifi-
       cate.

       When mail is sent to the public MX host  for  the  recipient's  domain,
       server certificates are by default optional, and delivery proceeds even
       if certificate verification fails. For delivery via a  submission  ser-
       vice  that  requires SASL authentication, it may be appropriate to send
       plaintext passwords only when the connection to the server is  strongly
       encrypted and the server identity is verified.

       The smtp_sasl_tls_verified_security_options parameter makes it possible
       to only enable plaintext mechanisms when a  secure  connection  to  the
       server  is  available.  Submission  servers subject to this policy must
       either have verifiable certificates  or  offer  suitable  non-plaintext
       SASL mechanisms.

       This feature is available in Postfix 2.6 and later.

smtp_sasl_type (default: cyrus)
       The  SASL  plug-in  type  that  the  Postfix SMTP client should use for
       authentication.  The available types are listed with the "postconf  -A"
       command.

       This feature is available in Postfix 2.3 and later.

smtp_send_dummy_mail_auth (default: no)
       Whether  or not to append the "AUTH=<>" option to the MAIL FROM command
       in SASL-authenticated SMTP sessions. The default is not to  send  this,
       to  avoid problems with broken remote SMTP servers.  Before Postfix 2.9
       the behavior is as if "smtp_send_dummy_mail_auth = yes".

       This feature is available in Postfix 2.9 and later.

smtp_send_xforward_command (default: no)
       Send the non-standard XFORWARD command when  the  Postfix  SMTP  server
       EHLO response announces XFORWARD support.

       This allows a Postfix SMTP delivery agent, used for injecting mail into
       a content filter, to forward the name, address, protocol and HELO  name
       of  the  original  client  to the content filter and downstream queuing
       SMTP  server.  This  can  produce  more  useful  logging  than   local-
       host[127.0.0.1] etc.

       This feature is available in Postfix 2.1 and later.

smtp_sender_dependent_authentication (default: no)
       Enable sender-dependent authentication in the Postfix SMTP client; this
       is available only with SASL authentication, and disables  SMTP  connec-
       tion  caching  to  ensure that mail from different senders will use the
       appropriate credentials.

       This feature is available in Postfix 2.3 and later.

smtp_skip_4xx_greeting (default: yes)
       Skip SMTP servers that greet with a 4XX status code (go away, try again
       later).

       By  default,  the Postfix SMTP client moves on the next mail exchanger.
       Specify "smtp_skip_4xx_greeting = no" if Postfix should defer  delivery
       immediately.

       This  feature  is  available in Postfix 2.0 and earlier.  Later Postfix
       versions always skip remote SMTP servers that greet with a  4XX  status
       code.

smtp_skip_5xx_greeting (default: yes)
       Skip remote SMTP servers that greet with a 5XX status code.

       By  default,  the Postfix SMTP client moves on the next mail exchanger.
       Specify "smtp_skip_5xx_greeting = no" if Postfix should bounce the mail
       immediately.  Caution:  the  latter  behavior appears to contradict RFC
       2821.

smtp_skip_quit_response (default: yes)
       Do not wait for the response to the SMTP QUIT command.

smtp_starttls_timeout (default: 300s)
       Time limit for Postfix SMTP client write and read operations during TLS
       startup and shutdown handshake procedures.

       This feature is available in Postfix 2.2 and later.

smtp_tls_CAfile (default: empty)
       A  file  containing  CA certificates of root CAs trusted to sign either
       remote SMTP server certificates or intermediate CA certificates.  These
       are  loaded  into  memory  before  the smtp(8) client enters the chroot
       jail.  If  the  number  of  trusted  roots  is  large,  consider  using
       smtp_tls_CApath  instead,  but  note  that the latter directory must be
       present in the chroot jail if the smtp(8) client is chrooted. This file
       may  also be used to augment the client certificate trust chain, but it
       is  best  to  include  all  the  required  certificates   directly   in
       $smtp_tls_cert_file.

       Specify  "smtp_tls_CAfile  =  /path/to/system_CA_file"  to use ONLY the
       system-supplied default Certification Authority certificates.

       Specify "tls_append_default_CA = no" to prevent Postfix from  appending
       the  system-supplied default CAs and trusting third-party certificates.

       Example:

       smtp_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_CApath (default: empty)
       Directory with PEM format Certification Authority certificates that the
       Postfix  SMTP  client  uses to verify a remote SMTP server certificate.
       Don't forget to create the necessary "hash" links  with,  for  example,
       "$OPENSSL_HOME/bin/c_rehash /etc/postfix/certs".

       To  use  this option in chroot mode, this directory (or a copy) must be
       inside the chroot jail.

       Specify "smtp_tls_CApath = /path/to/system_CA_directory"  to  use  ONLY
       the system-supplied default Certification Authority certificates.

       Specify  "tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party  certificates.

       Example:

       smtp_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

smtp_tls_block_early_mail_reply (default: no)
       Try  to detect a mail hijacking attack based on a TLS protocol vulnera-
       bility (CVE-2009-3555), where  an  attacker  prepends  malicious  HELO,
       MAIL,  RCPT,  DATA  commands to a Postfix SMTP client TLS session.  The
       attack would succeed with non-Postfix SMTP servers that  reply  to  the
       malicious HELO, MAIL, RCPT, DATA commands after negotiating the Postfix
       SMTP client TLS session.

       This feature is available in Postfix 2.7.

smtp_tls_cert_file (default: empty)
       File with the Postfix SMTP client RSA certificate in PEM format.   This
       file  may  also  contain  the  Postfix SMTP client private RSA key, and
       these may be the same as the Postfix SMTP server  RSA  certificate  and
       key file.

       Do not configure client certificates unless you must present client TLS
       certificates to one or more servers. Client certificates are  not  usu-
       ally  needed,  and  can cause problems in configurations that work well
       without them. The recommended setting is to let the defaults stand:

           smtp_tls_cert_file =
           smtp_tls_key_file =
           smtp_tls_dcert_file =
           smtp_tls_dkey_file =
           smtp_tls_eccert_file =
           smtp_tls_eckey_file =

       The best way to use the default settings is to comment  out  the  above
       parameters in main.cf if present.

       To  enable  remote  SMTP servers to verify the Postfix SMTP client cer-
       tificate, the issuing CA certificates must be  made  available  to  the
       server. You should include the required certificates in the client cer-
       tificate file, the client certificate first,  then  the  issuing  CA(s)
       (bottom-up order).

       Example: the certificate for "client.example.com" was issued by "inter-
       mediate CA" which itself has a certificate issued by "root CA".  Create
       the  client.pem  file  with  "cat  client_cert.pem  intermediate_CA.pem
       root_CA.pem > client.pem".

       If you also want to verify remote SMTP server  certificates  issued  by
       these  CAs,  you can add the CA certificates to the smtp_tls_CAfile, in
       which case it is not necessary to have them in the  smtp_tls_cert_file,
       smtp_tls_dcert_file or smtp_tls_eccert_file.

       A certificate supplied here must be usable as an SSL client certificate
       and hence pass the "openssl verify -purpose sslclient ..." test.

       Example:

       smtp_tls_cert_file = /etc/postfix/client.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_cipherlist (default: empty)
       Obsolete Postfix < 2.3 control for the Postfix SMTP client  TLS  cipher
       list. As this feature applies to all TLS security levels, it is easy to
       create interoperability problems by choosing a non-default cipher list.
       Do not use a non-default TLS cipher list on hosts that deliver email to
       the public Internet: you will be unable to send email to  servers  that
       only  support  the  ciphers you exclude. Using a restricted cipher list
       may be more appropriate for an internal MTA, where one can  exert  some
       control over the TLS software and settings of the peer servers.

       Note: do not use "" quotes around the parameter value.

       This  feature  is available in Postfix version 2.2. It is not used with
       Postfix 2.3 and later; use smtp_tls_mandatory_ciphers instead.

smtp_tls_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP client will use with
       opportunistic     TLS    encryption.    Cipher    types    listed    in
       smtp_tls_exclude_ciphers are excluded from the base definition  of  the
       selected  cipher  grade.    The  default  value is "medium" for Postfix
       releases after the middle of 2015, "export" for older releases.

       When  TLS  is  mandatory  the  cipher   grade   is   chosen   via   the
       smtp_tls_mandatory_ciphers  configuration parameter, see there for syn-
       tax details. See smtp_tls_policy_maps for information on how to config-
       ure ciphers on a per-destination basis.

       This  feature is available in Postfix 2.6 and later. With earlier Post-
       fix releases only the smtp_tls_mandatory_ciphers  parameter  is  imple-
       mented, and opportunistic TLS always uses "export" or better (i.e. all)
       ciphers.

smtp_tls_dane_insecure_mx_policy (default: dane)
       The TLS policy for MX hosts with "secure" TLSA records when the nexthop
       destination  security level is dane, but the MX record was found via an
       "insecure" MX lookup.  The choices are:

       may    The TLSA records will be ignored and TLS will be  optional.   If
              the MX host does not appear to support STARTTLS, or the STARTTLS
              handshake fails, mail may be sent in the clear.

       encrypt
              The TLSA records will signal a requirement to  use  TLS.   While
              TLS encryption will be required, authentication will not be per-
              formed.

       dane (default)
              The TLSA records will be used just as with "secure" MX  records.
              TLS  encryption  will  be  required, and, if at least one of the
              TLSA records is "usable", authentication will be required.  When
              authentication  succeeds,  it  will be logged only as "Trusted",
              not "Verified", because the MX host name could have been forged.
              Though with "insecure" MX records an active attacker can compro-
              mise SMTP transport security by  returning  forged  MX  records,
              such  attacks are "tamper-evident" since any forged MX hostnames
              will be recorded in the mail logs.  Attackers who place  a  high
              value staying hidden may be deterred from forging MX records.

       This  feature  is available in Postfix 3.1 and later. The may policy is
       backwards-compatible with earlier Postfix versions.

smtp_tls_dcert_file (default: empty)
       File with the Postfix SMTP client DSA certificate in PEM format.   This
       file may also contain the Postfix SMTP client private DSA key.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_dcert_file = /etc/postfix/client-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtp_tls_dkey_file (default: $smtp_tls_dcert_file)
       File  with the Postfix SMTP client DSA private key in PEM format.  This
       file may be combined with the Postfix SMTP client DSA certificate  file
       specified with $smtp_tls_dcert_file.

       The  private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtp_tls_eccert_file (default: empty)
       File  with  the  Postfix  SMTP  client ECDSA certificate in PEM format.
       This file may also contain the Postfix SMTP client ECDSA private key.

       See the discussion under smtp_tls_cert_file for more details.

       Example:

       smtp_tls_eccert_file = /etc/postfix/ecdsa-ccert.pem

       This feature is available in Postfix 2.6 and  later,  when  Postfix  is
       compiled and linked with OpenSSL 1.0.0 or later.

smtp_tls_eckey_file (default: $smtp_tls_eccert_file)
       File  with  the  Postfix  SMTP  client ECDSA private key in PEM format.
       This file may be combined with the Postfix SMTP client  ECDSA  certifi-
       cate file specified with $smtp_tls_eccert_file.

       The  private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This  feature  is  available  in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

smtp_tls_enforce_peername (default: yes)
       With mandatory TLS encryption, require  that  the  remote  SMTP  server
       hostname matches the information in the remote SMTP server certificate.
       As of RFC 2487 the requirements for hostname checking for  MTA  clients
       are not specified.

       This  option  can  be set to "no" to disable strict peer name checking.
       This setting has no effect on sessions  that  are  controlled  via  the
       smtp_tls_per_site table.

       Disabling  the  hostname verification can make sense in closed environ-
       ment where special CAs are created.  If not used carefully, this option
       opens  the  danger  of  a "man-in-the-middle" attack (the CommonName of
       this attacker will be logged).

       This feature is available in Postfix 2.2 and later.  With  Postfix  2.3
       and later use smtp_tls_security_level instead.

smtp_tls_exclude_ciphers (default: empty)
       List of ciphers or cipher types to exclude from the Postfix SMTP client
       cipher list at  all  TLS  security  levels.  This  is  not  an  OpenSSL
       cipherlist,  it is a simple list separated by whitespace and/or commas.
       The elements are a single cipher, or one or more "+"  separated  cipher
       properties,  in which case only ciphers matching all the properties are
       excluded.

       Examples (some of these will cause problems):

           smtp_tls_exclude_ciphers = aNULL
           smtp_tls_exclude_ciphers = MD5, DES
           smtp_tls_exclude_ciphers = DES+MD5
           smtp_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
           smtp_tls_exclude_ciphers = kEDH+aRSA

       The first setting, disables anonymous ciphers. The  next  setting  dis-
       ables  ciphers  that  use  the MD5 digest algorithm or the (single) DES
       encryption algorithm. The next setting disables ciphers  that  use  MD5
       and   DES   together.   The  next  setting  disables  the  two  ciphers
       "AES256-SHA" and "DES-CBC3-MD5". The last setting disables ciphers that
       use "EDH" key exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtp_tls_fingerprint_cert_match (default: empty)
       List  of acceptable remote SMTP server certificate fingerprints for the
       "fingerprint" TLS security  level  (smtp_tls_security_level  =  finger-
       print). At this security level, Certification Authorities are not used,
       and certificate expiration times are ignored. Instead, server  certifi-
       cates are verified directly via their certificate fingerprint or public
       key fingerprint (Postfix 2.9 and later). The fingerprint is  a  message
       digest  of the server certificate (or public key). The digest algorithm
       is selected via the smtp_tls_fingerprint_digest parameter.

       When an smtp_tls_policy_maps table entry  specifies  the  "fingerprint"
       security  level,  any "match" attributes in that entry specify the list
       of valid fingerprints for the corresponding destination. Multiple  fin-
       gerprints  can  be  combined  with  a  "|"  delimiter in a single match
       attribute, or multiple match attributes can be employed.

       Example: Certificate fingerprint verification  with  internal  mailhub.
       Two  matching  fingerprints  are  listed. The relayhost may be multiple
       physical hosts behind a load-balancer, each with its own private/public
       key  and self-signed certificate. Alternatively, a single relayhost may
       be in the process of switching from one set of private/public  keys  to
       another, and both keys are trusted just prior to the transition.

           relayhost = [mailhub.example.com]
           smtp_tls_security_level = fingerprint
           smtp_tls_fingerprint_digest = md5
           smtp_tls_fingerprint_cert_match =
               3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
               EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       Example:  Certificate  fingerprint  verification with selected destina-
       tions.  As in the example above, we show two matching fingerprints:

           /etc/postfix/main.cf:
               smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
               smtp_tls_fingerprint_digest = md5

           /etc/postfix/tls_policy:
               example.com fingerprint
                   match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
                   match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.5 and later.

smtp_tls_fingerprint_digest (default: md5)
       The message digest algorithm used to construct remote SMTP server  cer-
       tificate   fingerprints.   At  the  "fingerprint"  TLS  security  level
       (smtp_tls_security_level = fingerprint), the server certificate is ver-
       ified  by  directly  matching its certificate fingerprint or its public
       key fingerprint (Postfix 2.9 and later). The fingerprint is the message
       digest of the server certificate (or its public key) using the selected
       algorithm. With a digest  algorithm  resistant  to  "second  pre-image"
       attacks,  it  is not feasible to create a new public key and a matching
       certificate (or public/private key-pair) that has the same fingerprint.

       The  default  algorithm  is  md5; this is consistent with the backwards
       compatible setting of the digest used to verify client certificates  in
       the SMTP server.

       The  best practice algorithm is now sha1. Recent advances in hash func-
       tion cryptanalysis have led to md5 being deprecated in favor  of  sha1.
       However,  as  long  as  there  are  no known "second pre-image" attacks
       against md5, its use in this context can still be considered safe.

       While additional digest algorithms are often available  with  OpenSSL's
       libcrypto, only those used by libssl in SSL cipher suites are available
       to Postfix. For now this means just md5 or sha1.

       To find the fingerprint of a specific certificate file, with a specific
       digest algorithm, run:

           $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The  text  to  the  right  of "=" sign is the desired fingerprint.  For
       example:

           $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
           SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       To extract the public key fingerprint from an  X.509  certificate,  you
       need  to  extract  the  public key from the certificate and compute the
       appropriate digest of its DER (ASN.1) encoding. With OpenSSL the "-pub-
       key"  option  of  the  "x509" command extracts the public key always in
       "PEM" format. We pipe the result to another OpenSSL command  that  con-
       verts the key to DER and then to the "dgst" command to compute the fin-
       gerprint.

       The actual command to transform the key to DER format  depends  on  the
       version  of OpenSSL used. With OpenSSL 1.0.0 and later, the "pkey" com-
       mand supports all key types. With OpenSSL 0.9.8 and  earlier,  the  key
       type  is  always  RSA  (nobody uses DSA, and EC keys are not fully sup-
       ported by 0.9.8), so the "rsa" command is used.

           # OpenSSL 1.0 with all certificates and SHA-1 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl pkey -pubin -outform DER |
               openssl dgst -sha1 -c
           (stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:8b:fc:09:1a:61:98:b5:bc:7c:60:58

           # OpenSSL 0.9.8 with RSA certificates and MD5 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl rsa -pubin -outform DER |
               openssl dgst -md5 -c
           (stdin)= f4:62:60:f6:12:8f:d5:8d:28:4d:13:a7:db:b2:ff:50

       The Postfix SMTP server and client log the peer (leaf) certificate fin-
       gerprint  and  public  key  fingerprint  when  the TLS loglevel is 2 or
       higher.

       Note: Postfix 2.9.0-2.9.5 computed the public  key  fingerprint  incor-
       rectly.  To  use  public-key  fingerprints, upgrade to Postfix 2.9.6 or
       later.

       This feature is available in Postfix 2.5 and later.

smtp_tls_force_insecure_host_tlsa_lookup (default: no)
       Lookup the associated DANE TLSA RRset even when a hostname  is  not  an
       alias  and  its  address  records  lie  in  an  unsigned zone.  This is
       unlikely to ever yield DNSSEC validated results, since child  zones  of
       unsigned  zones are also unsigned in the absence of DLV or locally con-
       figured non-root trust-anchors.  We  anticipate  that  such  mechanisms
       will  not be used for just the "_tcp" subdomain of a host.  Suppressing
       the TLSA RRset lookup reduces latency and avoids  potential  interoper-
       ability  problems with nameservers for unsigned zones that are not pre-
       pared to handle the new TLSA RRset.

       This feature is available in Postfix 2.11.

smtp_tls_key_file (default: $smtp_tls_cert_file)
       File with the Postfix SMTP client RSA private key in PEM format.   This
       file  may be combined with the Postfix SMTP client RSA certificate file
       specified with $smtp_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       Example:

       smtp_tls_key_file = $smtp_tls_cert_file

       This feature is available in Postfix 2.2 and later.

smtp_tls_loglevel (default: 0)
       Enable additional Postfix SMTP client logging of  TLS  activity.   Each
       logging  level  also includes the information that is logged at a lower
       logging level.

              0 Disable logging of TLS activity.

              1 Log only a summary message on TLS handshake  completion  -  no
              logging  of remote SMTP server certificate trust-chain verifica-
              tion errors if server certificate verification is not  required.
              With Postfix 2.8 and earlier, log the summary message and uncon-
              ditionally log trust-chain verification errors.

              2 Also log levels during TLS negotiation.

              3 Also  log  hexadecimal  and  ASCII  dump  of  TLS  negotiation
              process.

              4  Also  log hexadecimal and ASCII dump of complete transmission
              after STARTTLS.

       Do not use "smtp_tls_loglevel = 2" or higher except in  case  of  prob-
       lems. Use of loglevel 4 is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtp_tls_mandatory_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP client will use with
       mandatory TLS encryption.  The default value "medium" is  suitable  for
       most destinations with which you may want to enforce TLS, and is beyond
       the reach of today's cryptanalytic  methods.  See  smtp_tls_policy_maps
       for information on how to configure ciphers on a per-destination basis.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or better OpenSSL ciphers.  The underlying
              cipherlist is specified via the tls_export_cipherlist configura-
              tion parameter, which you are strongly encouraged to not change.
              This choice is insecure and SHOULD NOT be used.

       low    Enable  "LOW"  grade  or better OpenSSL ciphers.  The underlying
              cipherlist is specified via the tls_low_cipherlist configuration
              parameter,  which  you  are  strongly  encouraged to not change.
              This choice is insecure and SHOULD NOT be used.

       medium Enable "MEDIUM" grade or better OpenSSL ciphers.  The underlying
              cipherlist is specified via the tls_medium_cipherlist configura-
              tion parameter, which you are strongly encouraged to not change.

       high   Enable  only  "HIGH" grade OpenSSL ciphers.  This setting may be
              appropriate when all mandatory TLS destinations (e.g.  when  all
              mail is routed to a suitably capable relayhost) support at least
              one "HIGH" grade cipher. The underlying cipherlist is  specified
              via  the  tls_high_cipherlist configuration parameter, which you
              are strongly encouraged to not change.

       null   Enable only the "NULL" OpenSSL ciphers, these provide  authenti-
              cation  without encryption.  This setting is only appropriate in
              the rare case that all servers are prepared to use NULL  ciphers
              (not  normally  enabled in TLS servers). A plausible use-case is
              an LMTP server listening on a UNIX-domain socket that is config-
              ured  to  support  "NULL"  ciphers. The underlying cipherlist is
              specified via the tls_null_cipherlist  configuration  parameter,
              which you are strongly encouraged to not change.

       The  underlying cipherlists for grades other than "null" include anony-
       mous ciphers, but these are automatically filtered out if  the  Postfix
       SMTP  client is configured to verify server certificates.  You are very
       unlikely to need to take any steps to exclude anonymous  ciphers,  they
       are excluded automatically as necessary.  If you must exclude anonymous
       ciphers at the "may" or "encrypt" security  levels,  when  the  Postfix
       SMTP   client   does   not   need   or   use   peer  certificates,  set
       "smtp_tls_exclude_ciphers = aNULL". To exclude anonymous  ciphers  only
       when TLS is enforced, set "smtp_tls_mandatory_exclude_ciphers = aNULL".

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_exclude_ciphers (default: empty)
       Additional list of ciphers or cipher types to exclude from the  Postfix
       SMTP  client  cipher  list  at mandatory TLS security levels. This list
       works    in    addition    to    the     exclusions     listed     with
       smtp_tls_exclude_ciphers (see there for syntax details).

       Starting with Postfix 2.6, the mandatory cipher exclusions can be spec-
       ified  on  a  per-destination  basis  via  the  TLS  policy   "exclude"
       attribute. See smtp_tls_policy_maps for notes and examples.

       This feature is available in Postfix 2.3 and later.

smtp_tls_mandatory_protocols (default: !SSLv2, !SSLv3)
       List  of  SSL/TLS  protocols that the Postfix SMTP client will use with
       mandatory TLS encryption.  In  main.cf  the  values  are  separated  by
       whitespace, commas or colons. In the policy table "protocols" attribute
       (see smtp_tls_policy_maps) the only valid separator is colon. An  empty
       value  means allow all protocols. The valid protocol names, (see \fBfBSSL_get_version(3)
       ), are "SSLv2",  "SSLv3"  and  "TLSv1".  The  default
       value  is  "!SSLv2,  !SSLv3"  for  Postfix releases after the middle of
       2015, "!SSLv2" for older releases.

       With Postfix >= 2.5 the parameter syntax was expanded to support proto-
       col   exclusions.   One  can  explicitly  exclude  "SSLv2"  by  setting
       "smtp_tls_mandatory_protocols = !SSLv2". To exclude  both  "SSLv2"  and
       "SSLv3"  set  "smtp_tls_mandatory_protocols  = !SSLv2, !SSLv3". Listing
       the protocols to include, rather than protocols  to  exclude,  is  sup-
       ported,  but  not  recommended. The exclusion form more closely matches
       the underlying OpenSSL interface semantics.

       The range of protocols advertised by an SSL/TLS client must be contigu-
       ous.   When a protocol version is enabled, disabling any higher version
       implicitly disables all versions above that higher version.  Thus,  for
       example:

           smtp_tls_mandatory_protocols = !SSLv2, !TLSv1
       also  disables  any  protocols  version  higher than TLSv1 leaving only
       "SSLv3" enabled.

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1"  and
       "TLSv1.2".  When  Postfix  <=  2.5  is  linked against OpenSSL 1.0.1 or
       later, these, or any other new protocol versions,  cannot  be  disabled
       except by also disabling "TLSv1" (typically leaving just "SSLv3").  The
       latest patch levels of Postfix >= 2.6, and all versions of  Postfix  >=
       2.10 can explicitly disable support for "TLSv1.1" or "TLSv1.2".

       At the dane and dane-only security levels, when usable TLSA records are
       obtained for the remote SMTP server, the Postfix SMTP client  is  obli-
       gated to include the SNI TLS extension in its SSL client hello message.
       This may help the remote SMTP server live up to its promise to  provide
       a  certificate  that  matches  its  TLSA records.  Since TLS extensions
       require TLS 1.0 or later, the Postfix SMTP client must disable  "SSLv2"
       and  "SSLv3" when SNI is required.  If you use "dane" or "dane-only" do
       not disable TLSv1, except perhaps via the policy table for destinations
       which you are sure will support "TLSv1.1" or "TLSv1.2".

       See   the  documentation  of  the  smtp_tls_policy_maps  parameter  and
       TLS_README for more information about security levels.

       Example:

       # Preferred syntax with Postfix >= 2.5:
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       # Legacy syntax:
       smtp_tls_mandatory_protocols = TLSv1

       This feature is available in Postfix 2.3 and later.

smtp_tls_note_starttls_offer (default: no)
       Log the hostname of a remote SMTP server that offers STARTTLS, when TLS
       is not already enabled for that server.

       The logfile record looks like:

       postfix/smtp[pid]:  Host offered STARTTLS: [name.of.host]

       This feature is available in Postfix 2.2 and later.

smtp_tls_per_site (default: empty)
       Optional lookup tables with the Postfix SMTP client TLS usage policy by
       next-hop destination and by remote SMTP  server  hostname.   When  both
       lookups  succeed,  the  more specific per-site policy (NONE, MUST, etc)
       overrides the less specific one (MAY), and  the  more  secure  per-site
       policy  (MUST, etc) overrides the less secure one (NONE).  With Postfix
       2.3  and  later  smtp_tls_per_site   is   strongly   discouraged:   use
       smtp_tls_policy_maps instead.

       Use  of  the bare hostname as the per-site table lookup key is discour-
       aged. Always use the full destination nexthop (enclosed in  []  with  a
       possible  ":port"  suffix).  A recipient domain or MX-enabled transport
       next-hop with no port suffix may look like  a  bare  hostname,  but  is
       still a suitable destination.

       Specify  a  next-hop  destination  or  server hostname on the left-hand
       side; no wildcards are allowed. The next-hop destination is either  the
       recipient  domain, or the destination specified with a transport(5) ta-
       ble, the relayhost parameter, or the relay_transport parameter.  On the
       right hand side specify one of the following keywords:

       NONE   Don't  use TLS at all. This overrides a less specific MAY lookup
              result from the alternate host or next-hop lookup key, and over-
              rides    the    global   smtp_use_tls,   smtp_enforce_tls,   and
              smtp_tls_enforce_peername settings.

       MAY    Try to use TLS if the server announces  support,  otherwise  use
              the unencrypted connection. This has less precedence than a more
              specific result (including NONE)  from  the  alternate  host  or
              next-hop  lookup key, and has less precedence than the more spe-
              cific global "smtp_enforce_tls = yes" or "smtp_tls_enforce_peer-
              name = yes".

       MUST_NOPEERMATCH
              Require  TLS encryption, but do not require that the remote SMTP
              server hostname matches  the  information  in  the  remote  SMTP
              server certificate, or that the server certificate was issued by
              a trusted CA. This overrides a less secure NONE or a  less  spe-
              cific  MAY  lookup  result  from  the alternate host or next-hop
              lookup   key,   and   overrides   the    global    smtp_use_tls,
              smtp_enforce_tls and smtp_tls_enforce_peername settings.

       MUST   Require  TLS  encryption,  require  that  the remote SMTP server
              hostname matches the information in the remote SMTP server  cer-
              tificate,  and  require  that the remote SMTP server certificate
              was issued by a trusted CA. This overrides a  less  secure  NONE
              and  MUST_NOPEERMATCH  or a less specific MAY lookup result from
              the alternate host or next-hop lookup  key,  and  overrides  the
              global smtp_use_tls, smtp_enforce_tls and smtp_tls_enforce_peer-
              name settings.

       The above keywords correspond to the "none", "may", "encrypt" and "ver-
       ify"  security  levels  for  the  new smtp_tls_security_level parameter
       introduced in Postfix 2.3. Starting with Postfix 2.3, and independently
       of  how  the  policy  is  specified, the smtp_tls_mandatory_ciphers and
       smtp_tls_mandatory_protocols parameters apply when  TLS  encryption  is
       mandatory.  Connections  for  which  encryption  is  optional typically
       enable all "export" grade and better ciphers (see smtp_tls_ciphers  and
       smtp_tls_protocols).

       As long as no secure DNS lookup mechanism is available, false hostnames
       in MX or CNAME responses can change the server  hostname  that  Postfix
       uses  for  TLS  policy lookup and server certificate verification. Even
       with a perfect match between the server hostname and  the  server  cer-
       tificate,  there is no guarantee that Postfix is connected to the right
       server.  See TLS_README (Closing a DNS loophole with obsolete  per-site
       TLS policies) for a possible work-around.

       This  feature  is  available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtp_tls_policy_maps instead.

smtp_tls_policy_maps (default: empty)
       Optional lookup tables with the Postfix SMTP client TLS security policy
       by  next-hop  destination;  when  a  non-empty value is specified, this
       overrides the obsolete smtp_tls_per_site parameter.  See TLS_README for
       a more detailed discussion of TLS security levels.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       The TLS policy table is indexed by the full next-hop destination, which
       is either the recipient domain, or the verbatim next-hop  specified  in
       the     transport    table,    $local_transport,    $virtual_transport,
       $relay_transport or $default_transport.  This  includes  any  enclosing
       square brackets and any non-default destination server port suffix. The
       LMTP socket type prefix (inet: or unix:) is not included in the  lookup
       key.

       Only  the  next-hop  domain,  or $myhostname with LMTP over UNIX-domain
       sockets, is used as the nexthop name for certificate verification.  The
       port  and  any  enclosing  square brackets are used in the table lookup
       key, but are not used for server name verification.

       When the lookup key is a domain name without enclosing square  brackets
       or  any  :port  suffix  (typically  the recipient domain), and the full
       domain is not found in the table, just as with the transport(5)  table,
       the  parent  domain starting with a leading "." is matched recursively.
       This allows one to specify a security policy for a recipient domain and
       all its sub-domains.

       The  lookup result is a security level, followed by an optional list of
       whitespace and/or comma separated name=value attributes  that  override
       related  main.cf settings. The TLS security levels in order of increas-
       ing security are:

       none   No TLS. No additional attributes are supported at this level.

       may    Opportunistic TLS. Since sending in  the  clear  is  acceptable,
              demanding  stronger  than  default  TLS  security merely reduces
              interoperability. The optional "ciphers", "exclude" and  "proto-
              cols"  attributes  (available for opportunistic TLS with Postfix
              >=       2.6)       override       the       "smtp_tls_ciphers",
              "smtp_tls_exclude_ciphers"  and  "smtp_tls_protocols" configura-
              tion parameters. When opportunistic TLS handshakes fail, Postfix
              retries  the  connection  with  TLS  disabled.  This allows mail
              delivery to sites with non-interoperable TLS implementations.

       encrypt
              Mandatory TLS encryption. At this level and higher, the optional
              "protocols"  attribute  overrides  the  main.cf  smtp_tls_manda-
              tory_protocols parameter, the optional "ciphers" attribute over-
              rides  the main.cf smtp_tls_mandatory_ciphers parameter, and the
              optional "exclude" attribute  (Postfix  >=  2.6)  overrides  the
              main.cf  smtp_tls_mandatory_exclude_ciphers  parameter.  In  the
              policy table, multiple protocols or  excluded  ciphers  must  be
              separated  by colons, as attribute values may not contain white-
              space or commas.

       dane   Opportunistic DANE TLS.  The TLS policy for the  destination  is
              obtained  via  TLSA  records  in DNSSEC.  If no TLSA records are
              found, the effective  security  level  used  is  may.   If  TLSA
              records  are  found, but none are usable, the effective security
              level is encrypt.  When usable TLSA records are obtained for the
              remote  SMTP  server, the server certificate must match the TLSA
              records.  RFC 6698 (DANE) TLS authentication and DNSSEC  support
              is available with Postfix 2.11 and later.

       dane-only
              Mandatory  DANE  TLS.   The  TLS  policy  for the destination is
              obtained via TLSA records in DNSSEC.  If  no  TLSA  records  are
              found,  or none are usable, no connection is made to the server.
              When usable TLSA  records  are  obtained  for  the  remote  SMTP
              server, the server certificate must match the TLSA records.  RFC
              6698 (DANE) TLS authentication and DNSSEC support  is  available
              with Postfix 2.11 and later.

       fingerprint
              Certificate fingerprint verification. Available with Postfix 2.5
              and later. At this security level, there are no trusted Certifi-
              cation  Authorities.  The  certificate  trust  chain, expiration
              date,  ...  are  not  checked.  Instead,  the   optional   match
              attribute,  or  else the main.cf smtp_tls_fingerprint_cert_match
              parameter, lists the certificate fingerprints or the public  key
              fingerprint (Postfix 2.9 and later) of the valid server certifi-
              cate. The digest algorithm used to calculate the fingerprint  is
              selected  by the smtp_tls_fingerprint_digest parameter. Multiple
              fingerprints can be combined with a "|" delimiter  in  a  single
              match  attribute,  or multiple match attributes can be employed.
              The ":" character is not  used  as  a  delimiter  as  it  occurs
              between each pair of fingerprint (hexadecimal) digits.

       verify Mandatory  TLS  verification.   At  this  security level, DNS MX
              lookups are trusted to be secure enough, and the  name  verified
              in  the  server  certificate  is usually obtained indirectly via
              unauthenticated DNS MX lookups.  The optional "match"  attribute
              overrides  the  main.cf smtp_tls_verify_cert_match parameter. In
              the policy table, multiple match patterns and strategies must be
              separated by colons.  In practice explicit control over matching
              is more common with the "secure" policy, described below.

       secure Secure-channel TLS. At this  security  level,  DNS  MX  lookups,
              though  potentially  used  to  determine  the candidate next-hop
              gateway IP addresses, are not trusted to be  secure  enough  for
              TLS peername verification. Instead, the default name verified in
              the server certificate is obtained directly from  the  next-hop,
              or  is  explicitly  specified  via  the optional match attribute
              which overrides the main.cf  smtp_tls_secure_cert_match  parame-
              ter. In the policy table, multiple match patterns and strategies
              must be separated by colons.  The match attribute is most useful
              when multiple domains are supported by common server, the policy
              entries for additional domains specify matching  rules  for  the
              primary  domain  certificate.  While  transport  table overrides
              routing the secondary domains to the primary nexthop also  allow
              secure verification, they risk delivery to the wrong destination
              when domains change hands or are re-assigned  to  new  gateways.
              With  the  "match" attribute approach, routing is not perturbed,
              and mail is deferred if verification of a new MX host fails.

       Example:

       /etc/postfix/main.cf:
           smtp_tls_policy_maps = hash:/etc/postfix/tls_policy
           # Postfix 2.5 and later
           smtp_tls_fingerprint_digest = md5

       /etc/postfix/tls_policy:
           example.edu                 none
           example.mil                 may
           example.gov                 encrypt protocols=TLSv1
           example.com                 verify ciphers=high
           example.net                 secure
           .example.net                secure match=.example.net:example.net
           [mail.example.org]:587      secure match=nexthop
           # Postfix 2.5 and later
           [thumb.example.org]          fingerprint
               match=EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35
               match=3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1

       Note: The hostname strategy if  listed  in  a  non-default  setting  of
       smtp_tls_secure_cert_match  or in the match attribute in the policy ta-
       ble can render the secure level vulnerable to DNS forgery. Do  not  use
       the hostname strategy for secure-channel configurations in environments
       where DNS security is not assured.

       This feature is available in Postfix 2.3 and later.

smtp_tls_protocols (default: !SSLv2, !SSLv3)
       List of TLS protocols that the Postfix  SMTP  client  will  exclude  or
       include  with  opportunistic  TLS  encryption.  The  default  value  is
       "!SSLv2, !SSLv3"  for  Postfix  releases  after  the  middle  of  2015,
       "!SSLv2"  for  older  releases.  Before  Postfix  2.6, the Postfix SMTP
       client would use all protocols with opportunistic TLS.

       In main.cf the values are separated by whitespace, commas or colons. In
       the policy table (see smtp_tls_policy_maps) the only valid separator is
       colon. An empty value means allow all  protocols.  The  valid  protocol
       names, (see \fBfBSSL_get_version(3)), are "SSLv2", "SSLv3" and "TLSv1".

       The range of protocols advertised by an SSL/TLS client must be contigu-
       ous.   When a protocol version is enabled, disabling any higher version
       implicitly disables all versions above that higher version.  Thus,  for
       example:

           smtp_tls_mandatory_protocols = !SSLv2, !TLSv1
       also  disables  any  protocols  version  higher than TLSv1 leaving only
       "SSLv3" enabled.

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1"  and
       "TLSv1.2".  The latest patch levels of Postfix >= 2.6, and all versions
       of Postfix >= 2.10 can explicitly  disable  support  for  "TLSv1.1"  or
       "TLSv1.2"

       To  include  a  protocol  list its name, to exclude it, prefix the name
       with a "!" character.  To  exclude  SSLv2  for  opportunistic  TLS  set
       "smtp_tls_protocols  = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
       "smtp_tls_protocols = !SSLv2, !SSLv3". Explicitly listing the protocols
       to  include,  rather  than  protocols to exclude, is supported, but not
       recommended.  The exclusion form more closely  matches  the  underlying
       OpenSSL interface semantics.

       Example:
       # TLSv1 or better:
       smtp_tls_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.6 and later.

smtp_tls_scert_verifydepth (default: 9)
       The  verification depth for remote SMTP server certificates. A depth of
       1 is sufficient if the issuing CA is listed in a local CA file.

       The default verification depth is 9 (the OpenSSL default) for  compati-
       bility with earlier Postfix behavior. Prior to Postfix 2.5, the default
       value was 5, but the limit was not actually enforced. If you  have  set
       this  to  a  lower  non-default  value,  certificates with longer trust
       chains may now fail to verify. Certificate chains with 1 or 2  CAs  are
       common,  deeper  chains  are  more  rare and any number between 5 and 9
       should suffice in practice. You can choose a lower number if, for exam-
       ple,  you  trust  certificates directly signed by an issuing CA but not
       any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtp_tls_secure_cert_match (default: nexthop, dot-nexthop)
       How the Postfix SMTP client verifies the  server  certificate  peername
       for  the  "secure"  TLS  security level. In a "secure" TLS policy table
       ($smtp_tls_policy_maps) entry the optional "match" attribute  overrides
       this main.cf setting.

       This  parameter  specifies one or more patterns or strategies separated
       by commas, whitespace or colons.  In the policy table  the  only  valid
       separator is the colon character.

       For   a  description  of  the  pattern  and  strategy  syntax  see  the
       smtp_tls_verify_cert_match parameter. The "hostname" strategy should be
       avoided  in  this  context,  as  in the absence of a secure global DNS,
       using the results of MX lookups  in  certificate  verification  is  not
       immune to active (man-in-the-middle) attacks on DNS.

       Sample main.cf setting:

           smtp_tls_secure_cert_match = nexthop

       Sample policy table override:

           example.net     secure match=example.com:.example.com
           .example.net    secure match=example.com:.example.com

       This feature is available in Postfix 2.3 and later.

smtp_tls_security_level (default: empty)
       The default SMTP TLS security level for the Postfix SMTP client; when a
       non-empty value is specified, this overrides  the  obsolete  parameters
       smtp_use_tls, smtp_enforce_tls, and smtp_tls_enforce_peername.

       Specify one of the following security levels:

       none   No  TLS. TLS will not be used unless enabled for specific desti-
              nations via smtp_tls_policy_maps.

       may    Opportunistic TLS. Use TLS if this is supported  by  the  remote
              SMTP server, otherwise use plaintext. Since sending in the clear
              is acceptable, demanding  stronger  than  default  TLS  security
              merely  reduces  interoperability.   The  "smtp_tls_ciphers" and
              "smtp_tls_protocols" (Postfix >= 2.6)  configuration  parameters
              provide  control  over  the protocols and cipher grade used with
              opportunistic TLS.  With earlier releases the opportunistic  TLS
              cipher  grade  is always "export" and no protocols are disabled.
              When TLS handshakes fail, the connection  is  retried  with  TLS
              disabled.   This allows mail delivery to sites with non-interop-
              erable TLS implementations.

       encrypt
              Mandatory TLS encryption. Since a minimum level of  security  is
              intended,  it  is  reasonable  to be specific about sufficiently
              secure protocol versions and ciphers. At this security level and
              higher,  the main.cf parameters smtp_tls_mandatory_protocols and
              smtp_tls_mandatory_ciphers specify the TLS protocols and minimum
              cipher grade which the administrator considers secure enough for
              mandatory encrypted sessions. This  security  level  is  not  an
              appropriate default for systems delivering mail to the Internet.

       dane   Opportunistic DANE TLS.  At this security level, the TLS  policy
              for  the destination is obtained via DNSSEC.  For TLSA policy to
              be in effect, the destination domain's containing DNS zone  must
              be signed and the Postfix SMTP client's operating system must be
              configured to send its DNS queries to a recursive DNS nameserver
              that is able to validate the signed records.  Each MX host's DNS
              zone should also be signed, and should publish  DANE  TLSA  (RFC
              6698) records that specify how that MX host's TLS certificate is
              to be verified.  TLSA records do not preempt the normal SMTP  MX
              host selection algorithm, if some MX hosts support TLSA and oth-
              ers do not, TLS security will vary from  delivery  to  delivery.
              It  is  up  to  the domain owner to configure their MX hosts and
              their DNS sensibly.  To configure the Postfix  SMTP  client  for
              DNSSEC  lookups  see  the  documentation  for  the smtp_dns_sup-
              port_level  main.cf  parameter.   When   DNSSEC-validated   TLSA
              records are not found the effective tls security level is "may".
              When TLSA records are found, but are all unusable the  effective
              security  level  is  "encrypt".   For  purposes  of protocol and
              cipher selection, the "dane" security level is  treated  like  a
              "mandatory"  TLS  security level, and weak ciphers and protocols
              are disabled.  Since DANE authenticates server certificates  the
              "aNULL"  cipher-suites are transparently excluded at this level,
              no need to configure this manually.  RFC 6698 (DANE) TLS authen-
              tication is available with Postfix 2.11 and later.

       dane-only
              Mandatory  DANE  TLS.   This is just like "dane" above, but DANE
              TLSA authentication is required.  There is no fallback to  "may"
              or  "encrypt"  when  TLSA  records are missing or unusable.  RFC
              6698 (DANE) TLS authentication is available  with  Postfix  2.11
              and later.

       fingerprint
              Certificate  fingerprint  verification.  At this security level,
              there are no trusted Certification Authorities.  The certificate
              trust  chain,  expiration  date, etc., are not checked. Instead,
              the smtp_tls_fingerprint_cert_match parameter lists the certifi-
              cate  fingerprint  or  public  key  fingerprint (Postfix 2.9 and
              later) of the valid server  certificate.  The  digest  algorithm
              used   to   calculate   the   fingerprint  is  selected  by  the
              smtp_tls_fingerprint_digest parameter.  Available  with  Postfix
              2.5 and later.

       verify Mandatory  TLS  verification.  At  this  security  level, DNS MX
              lookups are trusted to be secure enough, and the  name  verified
              in  the  server  certificate  is usually obtained indirectly via
              unauthenticated DNS MX lookups.  The  smtp_tls_verify_cert_match
              parameter  controls how the server name is verified. In practice
              explicit control over matching is more common  at  the  "secure"
              level,  described below. This security level is not an appropri-
              ate default for systems delivering mail to the Internet.

       secure Secure-channel TLS.  At this security  level,  DNS  MX  lookups,
              though  potentially  used  to  determine  the candidate next-hop
              gateway IP addresses, are not trusted to be  secure  enough  for
              TLS peername verification. Instead, the default name verified in
              the server certificate is obtained from the next-hop  domain  as
              specified in the smtp_tls_secure_cert_match configuration param-
              eter. The default matching rule is  that  a  server  certificate
              matches when its name is equal to or is a sub-domain of the nex-
              thop domain. This security level is not an  appropriate  default
              for systems delivering mail to the Internet.

       Examples:

       # No TLS. Formerly: smtp_use_tls=no and smtp_enforce_tls=no.
       smtp_tls_security_level = none

       # Opportunistic TLS.
       smtp_tls_security_level = may
       # Postfix >= 2.6:
       # Do not tweak opportunistic ciphers or protocol unless it is essential
       # to do so (if a security vulnerability is found in the SSL library that
       # can be mitigated by disabling a particular protocol or raising the
       # cipher grade from "export" to "low" or "medium").
       smtp_tls_ciphers = export
       smtp_tls_protocols = !SSLv2, !SSLv3

       # Mandatory (high-grade) TLS encryption.
       smtp_tls_security_level = encrypt
       smtp_tls_mandatory_ciphers = high

       # Mandatory TLS verification of hostname or nexthop domain.
       smtp_tls_security_level = verify
       smtp_tls_mandatory_ciphers = high
       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       # Secure channel TLS with exact nexthop name match.
       smtp_tls_security_level = secure
       smtp_tls_mandatory_protocols = TLSv1
       smtp_tls_mandatory_ciphers = high
       smtp_tls_secure_cert_match = nexthop

       # Certificate fingerprint verification (Postfix >= 2.5).
       # The CA-less "fingerprint" security level only scales to a limited
       # number of destinations. As a global default rather than a per-site
       # setting, this is practical when mail for all recipients is sent
       # to a central mail hub.
       relayhost = [mailhub.example.com]
       smtp_tls_security_level = fingerprint
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       smtp_tls_mandatory_ciphers = high
       smtp_tls_fingerprint_cert_match =
           3D:95:34:51:24:66:33:B9:D2:40:99:C0:C1:17:0B:D1
           EC:3B:2D:B0:5B:B1:FB:6D:20:A3:9D:72:F6:8D:12:35

       This feature is available in Postfix 2.3 and later.

smtp_tls_session_cache_database (default: empty)
       Name  of  the file containing the optional Postfix SMTP client TLS ses-
       sion cache. Specify a database type that supports enumeration, such  as
       btree or sdbm; there is no need to support concurrent access.  The file
       is created if it does not exist. The smtp(8) daemon does not  use  this
       parameter  directly,  rather the cache is implemented indirectly in the
       tlsmgr(8) daemon. This means that per-smtp-instance master.cf overrides
       of  this  parameter  are  not  effective.  Note, that each of the cache
       databases supported by tlsmgr(8) daemon: $smtpd_tls_session_cache_data-
       base,  $smtp_tls_session_cache_database (and with Postfix 2.3 and later
       $lmtp_tls_session_cache_database), needs to be stored separately. It is
       not  at  this  time possible to store multiple caches in a single data-
       base.

       Note: dbm databases are not  suitable.  TLS  session  objects  are  too
       large.

       As  of version 2.5, Postfix no longer uses root privileges when opening
       this file. The file  should  now  be  stored  under  the  Postfix-owned
       data_directory. As a migration aid, an attempt to open the file under a
       non-Postfix directory is redirected to  the  Postfix-owned  data_direc-
       tory, and a warning is logged.

       Example:

       smtp_tls_session_cache_database = btree:/var/db/postfix/smtp_scache

       This feature is available in Postfix 2.2 and later.

smtp_tls_session_cache_timeout (default: 3600s)
       The  expiration  time of Postfix SMTP client TLS session cache informa-
       tion.  A cache cleanup is performed periodically  every  $smtp_tls_ses-
       sion_cache_timeout  seconds.  As with $smtp_tls_session_cache_database,
       this parameter is implemented in the  tlsmgr(8)  daemon  and  therefore
       per-smtp-instance master.cf overrides are not possible.

       As  of  Postfix 2.11 this setting cannot exceed 100 days.  If set <= 0,
       session caching is disabled.  If set to a positive value  less  than  2
       minutes, the minimum value of 2 minutes is used instead.

       This feature is available in Postfix 2.2 and later.

smtp_tls_trust_anchor_file (default: empty)
       Zero  or  more  PEM-format  files with trust-anchor certificates and/or
       public keys.  If the parameter is not empty the root CAs in CAfile  and
       CApath  are  no  longer  trusted.  Rather, the Postfix SMTP client will
       only trust certificate-chains signed by one of the  trust-anchors  con-
       tained  in  the  chosen files.  The specified trust-anchor certificates
       and public keys  are  not  subject  to  expiration,  and  need  not  be
       (self-signed) root CAs.  They may, if desired, be intermediate certifi-
       cates. Therefore, these certificates also may be found "in the  middle"
       of  the  trust  chain  presented  by  the  remote  SMTP server, and any
       untrusted issuing parent certificates will be ignored.  Specify a  list
       of pathnames separated by comma or whitespace.

       Whether  specified  in  main.cf,  or  on  a  per-destination basis, the
       trust-anchor PEM file must be accessible to the Postfix SMTP client  in
       the  chroot  jail  if applicable.  The trust-anchor file should contain
       only certificates and public keys, no private key material, and must be
       readable  by the non-privileged $mail_owner user.  This allows destina-
       tions to be bound to a set of  specific  CAs  or  public  keys  without
       trusting the same CAs for all destinations.

       The  main.cf  parameter  supports  single-purpose Postfix installations
       that send mail to a fixed  set  of  SMTP  peers.   At  most  sites,  if
       trust-anchor  files  are  used  at  all,  they  will  be specified on a
       per-destination basis via the "tafile" attribute of  the  "verify"  and
       "secure" levels in smtp_tls_policy_maps.

       The  underlying  mechanism is in support of RFC 6698 (DANE TLSA), which
       defines mechanisms for a client to securely determine server  TLS  cer-
       tificates via DNS.

       If  you want your trust anchors to be public keys, with OpenSSL you can
       extract a single PEM public key from a PEM X.509 file containing a sin-
       gle certificate, as follows:

           $ openssl x509 -in cert.pem -out ta-key.pem -noout -pubkey

       This feature is available in Postfix 2.11 and later.

smtp_tls_verify_cert_match (default: hostname)
       How  the  Postfix  SMTP client verifies the server certificate peername
       for the "verify" TLS security level. In a  "verify"  TLS  policy  table
       ($smtp_tls_policy_maps)  entry the optional "match" attribute overrides
       this main.cf setting.

       This parameter specifies one or more patterns or  strategies  separated
       by  commas,  whitespace  or colons.  In the policy table the only valid
       separator is the colon character.

       Patterns specify domain names, or domain name suffixes:

       example.com
              Match the example.com domain, i.e. one of the names  the  server
              certificate  must  be example.com, upper and lower case distinc-
              tions are ignored.

       .example.com
              Match subdomains of the example.com domain, i.e. match a name in
              the  server  certificate  that  consists of a non-zero number of
              labels followed by a .example.com suffix. Case distinctions  are
              ignored.

       Strategies  specify  a  transformation  from the next-hop domain to the
       expected name in the server certificate:

       nexthop
              Match against the next-hop domain, which is either the recipient
              domain,  or  the  transport  next-hop  configured for the domain
              stripped of any optional socket type  prefix,  enclosing  square
              brackets  and trailing port. When MX lookups are not suppressed,
              this is the original nexthop domain prior to the MX lookup,  not
              the  result  of the MX lookup. For LMTP delivery via UNIX-domain
              sockets, the verified next-hop name is $myhostname.  This strat-
              egy  is  suitable  for  use  with  the  "secure" policy. Case is
              ignored.

       dot-nexthop
              As above, but match server certificate names that are subdomains
              of the next-hop domain. Case is ignored.

       hostname
              Match  against the hostname of the server, often obtained via an
              unauthenticated DNS MX lookup. For LMTP delivery via UNIX-domain
              sockets, the verified name is $myhostname. This matches the ver-
              ification  strategy  of  the  "MUST"  keyword  in  the  obsolete
              smtp_tls_per_site  table, and is suitable for use with the "ver-
              ify" security level. When  the  next-hop  name  is  enclosed  in
              square  brackets to suppress MX lookups, the "hostname" strategy
              is the same as the "nexthop" strategy. Case is ignored.

       Sample main.cf setting:

       smtp_tls_verify_cert_match = hostname, nexthop, dot-nexthop

       Sample policy table override:

       example.com     verify  match=hostname:nexthop
       .example.com    verify  match=example.com:.example.com:hostname

       This feature is available in Postfix 2.3 and later.

smtp_tls_wrappermode (default: no)
       Request that the Postfix SMTP client connects using  the  legacy  SMTPS
       protocol instead of using the STARTTLS command.

       This mode requires "smtp_tls_security_level = encrypt" or stronger.

       Example:  deliver  all  remote mail via a provider's server "mail.exam-
       ple.com".

       /etc/postfix/main.cf:
           # Client-side SMTPS requires "encrypt" or stronger.
           smtp_tls_security_level = encrypt
           smtp_tls_wrappermode = yes
           # The [] suppress MX lookups.
           relayhost = [mail.example.com]:465

       More examples are in TLS_README, including examples for  older  Postfix
       versions.

       This feature is available in Postfix 3.0 and later.

smtp_use_tls (default: no)
       Opportunistic  mode: use TLS when a remote SMTP server announces START-
       TLS support, otherwise send the mail in the clear.  Beware:  some  SMTP
       servers  offer  STARTTLS  even if it is not configured.  With Postfix <
       2.3, if the TLS handshake fails, and  no  other  server  is  available,
       delivery  is deferred and mail stays in the queue. If this is a concern
       for you, use the smtp_tls_per_site feature instead.

       This feature is available in Postfix 2.2 and later.  With  Postfix  2.3
       and later use smtp_tls_security_level instead.

smtp_xforward_timeout (default: 300s)
       The  Postfix  SMTP  client time limit for sending the XFORWARD command,
       and for receiving the remote SMTP server response.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_authorized_verp_clients (default: $authorized_verp_clients)
       What  remote  SMTP  clients  are  allowed to specify the XVERP command.
       This command requests that mail be delivered one recipient  at  a  time
       with a per recipient return address.

       By default, no clients are allowed to specify XVERP.

       This  parameter was renamed with Postfix version 2.1. The default value
       is backwards compatible with Postfix version 2.0.

       Specify a list of network/netmask patterns, separated by commas  and/or
       whitespace.  The  mask specifies the number of bits in the network part
       of a host address. You can also specify hostnames or .domain names (the
       initial   dot   causes   the  domain  to  match  any  name  below  it),
       "/file/name" or  "type:table"  patterns.   A  "/file/name"  pattern  is
       replaced by its contents; a "type:table" lookup table is matched when a
       table entry matches a lookup string (the  lookup  result  is  ignored).
       Continue  long lines by starting the next line with whitespace. Specify
       "!pattern" to exclude an address or network block from  the  list.  The
       form  "!/file/name" is supported only in Postfix version 2.4 and later.

       Note: IP version 6 address information must be specified inside  []  in
       the  smtpd_authorized_verp_clients  value,  and in files specified with
       "/file/name".  IP version 6 addresses contain the  ":"  character,  and
       would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xclient_hosts (default: empty)
       What  remote SMTP clients are allowed to use the XCLIENT feature.  This
       command overrides remote SMTP  client  information  that  is  used  for
       access  control.  Typical use is for SMTP-based content filters, fetch-
       mail-like programs,  or  SMTP  server  access  rule  testing.  See  the
       XCLIENT_README document for details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XCLIENT.

       Specify  a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the  network  part
       of a host address. You can also specify hostnames or .domain names (the
       initial  dot  causes  the  domain  to  match  any   name   below   it),
       "/file/name"  or  "type:table"  patterns.   A  "/file/name"  pattern is
       replaced by its contents; a "type:table" lookup table is matched when a
       table  entry  matches  a  lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace.  Specify
       "!pattern"  to  exclude  an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and  later.

       Note:  IP  version 6 address information must be specified inside [] in
       the smtpd_authorized_xclient_hosts value, and in files  specified  with
       "/file/name".   IP  version  6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

smtpd_authorized_xforward_hosts (default: empty)
       What remote SMTP clients are allowed to use the XFORWARD feature.  This
       command  forwards  information  that  is  used to improve logging after
       SMTP-based  content  filters.  See  the  XFORWARD_README  document  for
       details.

       This feature is available in Postfix 2.1 and later.

       By default, no clients are allowed to specify XFORWARD.

       Specify  a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the  network  part
       of a host address. You can also specify hostnames or .domain names (the
       initial  dot  causes  the  domain  to  match  any   name   below   it),
       "/file/name"  or  "type:table"  patterns.   A  "/file/name"  pattern is
       replaced by its contents; a "type:table" lookup table is matched when a
       table  entry  matches  a  lookup string (the lookup result is ignored).
       Continue long lines by starting the next line with whitespace.  Specify
       "!pattern"  to  exclude  an address or network block from the list. The
       form "!/file/name" is supported only in Postfix version 2.4 and  later.

       Note:  IP  version 6 address information must be specified inside [] in
       the smtpd_authorized_xforward_hosts value, and in files specified  with
       "/file/name".   IP  version  6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

smtpd_banner (default: $myhostname ESMTP $mail_name)
       The text that follows the 220 status code in the SMTP greeting  banner.
       Some  people like to see the mail version advertised. By default, Post-
       fix shows no version.

       You MUST specify $myhostname at the start of the text. This is required
       by the SMTP protocol.

       Example:

       smtpd_banner = $myhostname ESMTP $mail_name ($mail_version)

smtpd_client_auth_rate_limit (default: 0)
       The  maximal number of AUTH commands that any client is allowed to send
       to this service per time unit, regardless of  whether  or  not  Postfix
       actually  accepts  those commands.  The time unit is specified with the
       anvil_rate_time_unit configuration parameter.

       By default, there is no limit on the number AUTH commands that a client
       may send.

       To disable this feature, specify a limit of 0.

       WARNING:  The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 3.1 and later.

smtpd_client_connection_count_limit (default: 50)
       How many simultaneous connections any client is allowed to make to this
       service.   By  default,  the  limit  is set to half the default process
       limit value.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not  be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

smtpd_client_connection_rate_limit (default: 0)
       The maximal number of connection attempts any client is allowed to make
       to this service per time unit.  The time unit  is  specified  with  the
       anvil_rate_time_unit configuration parameter.

       By  default,  a  client  can  make as many connections per time unit as
       Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not  be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_connection_rate_limit = 1000

smtpd_client_event_limit_exceptions (default: $mynetworks)
       Clients that are excluded from smtpd_client_*_count/rate_limit restric-
       tions. See the mynetworks parameter description for the parameter value
       syntax.

       By default, clients in trusted networks are excluded. Specify a list of
       network blocks, hostnames or .domain names (the initial dot causes  the
       domain to match any name below it).

       Note:  IP  version 6 address information must be specified inside [] in
       the smtpd_client_event_limit_exceptions value, and in  files  specified
       with  "/file/name".   IP version 6 addresses contain the ":" character,
       and would otherwise be confused with a "type:table" pattern.

       Pattern matching of domain names  is  controlled  by  the  presence  or
       absence    of   "smtpd_client_event_limit_exceptions"   in   the   par-
       ent_domain_matches_subdomains parameter value (postfix 3.0 and  later).

       This feature is available in Postfix 2.2 and later.

smtpd_client_message_rate_limit (default: 0)
       The  maximal  number  of  message  delivery requests that any client is
       allowed to make to this service per time unit, regardless of whether or
       not  Postfix  actually accepts those messages.  The time unit is speci-
       fied with the anvil_rate_time_unit configuration parameter.

       By default, a client can send as many  message  delivery  requests  per
       time unit as Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING:  The purpose of this feature is to limit abuse. It must not be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_message_rate_limit = 1000

smtpd_client_new_tls_session_rate_limit (default: 0)
       The maximal number of new (i.e., uncached) TLS sessions that  a  remote
       SMTP  client  is  allowed to negotiate with this service per time unit.
       The time unit is specified with the anvil_rate_time_unit  configuration
       parameter.

       By default, a remote SMTP client can negotiate as many new TLS sessions
       per time unit as Postfix can accept.

       To disable this feature, specify a limit of  0.  Otherwise,  specify  a
       limit that is at least the per-client concurrent session limit, or else
       legitimate client sessions may be rejected.

       WARNING: The purpose of this feature is to limit abuse. It must not  be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.3 and later.

       Example:

       smtpd_client_new_tls_session_rate_limit = 100

smtpd_client_port_logging (default: no)
       Enable  logging of the remote SMTP client port in addition to the host-
       name and IP address. The logging format is "host[address]:port".

       This feature is available in Postfix 2.5 and later.

smtpd_client_recipient_rate_limit (default: 0)
       The maximal number of recipient addresses that any client is allowed to
       send  to this service per time unit, regardless of whether or not Post-
       fix actually accepts those recipients.  The time unit is specified with
       the anvil_rate_time_unit configuration parameter.

       By default, a client can send as many recipient addresses per time unit
       as Postfix can accept.

       To disable this feature, specify a limit of 0.

       WARNING: The purpose of this feature is to limit abuse. It must not  be
       used to regulate legitimate mail traffic.

       This feature is available in Postfix 2.2 and later.

       Example:

       smtpd_client_recipient_rate_limit = 1000

smtpd_client_restrictions (default: empty)
       Optional  restrictions that the Postfix SMTP server applies in the con-
       text of a client connection request.  See SMTPD_ACCESS_README,  section
       "Delayed  evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       The default is to allow all connection requests.

       Specify a list of restrictions, separated by commas and/or  whitespace.
       Continue  long  lines  by  starting  the  next  line  with  whitespace.
       Restrictions are applied in the order as specified; the first  restric-
       tion that matches wins.

       The  following  restrictions  are specific to client hostname or client
       network address information.

       check_ccert_access type:table
              Use the remote SMTP client certificate fingerprint or the public
              key  fingerprint  (Postfix  2.9 and later) as lookup key for the
              specified access(5) database; with  Postfix  version  2.2,  also
              require that the remote SMTP client certificate is verified suc-
              cessfully.  The fingerprint digest algorithm is configurable via
              the  smtpd_tls_fingerprint_digest  parameter  (hard-coded as md5
              prior to Postfix version 2.5).  This feature is  available  with
              Postfix version 2.2 and later.

       check_client_access type:table
              Search  the  specified  access database for the client hostname,
              parent domains, client  IP  address,  or  networks  obtained  by
              stripping  least  significant  octets.  See the access(5) manual
              page for details.

       check_client_a_access type:table
              Search the specified access(5) database for the IP addresses for
              the  client  hostname,  and  execute  the  corresponding action.
              Note: a result of  "OK"  is  not  allowed  for  safety  reasons.
              Instead,  use  DUNNO  in  order  to  exclude specific hosts from
              blacklists.  This feature is available in Postfix 3.0 and later.

       check_client_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              client hostname, and execute the corresponding action.  Note:  a
              result  of  "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.   This
              feature is available in Postfix 2.7 and later.

       check_client_ns_access type:table
              Search  the specified access(5) database for the DNS servers for
              the client  hostname,  and  execute  the  corresponding  action.
              Note:  a  result  of  "OK"  is  not  allowed for safety reasons.
              Instead, use DUNNO in  order  to  exclude  specific  hosts  from
              blacklists.  This feature is available in Postfix 2.7 and later.

       check_reverse_client_hostname_access type:table
              Search the specified access database for the unverified  reverse
              client  hostname, parent domains, client IP address, or networks
              obtained  by  stripping  least  significant  octets.   See   the
              access(5)  manual  page  for details.  Note: a result of "OK" is
              not allowed for safety reasons.  Instead, use DUNNO in order  to
              exclude  specific hosts from blacklists.  This feature is avail-
              able in Postfix 2.6 and later.

       check_reverse_client_hostname_a_access type:table
              Search the specified access(5) database for the IP addresses for
              the  unverified  reverse client hostname, and execute the corre-
              sponding action.  Note: a result of  "OK"  is  not  allowed  for
              safety reasons.  Instead, use DUNNO in order to exclude specific
              hosts from blacklists.  This feature is available in Postfix 3.0
              and later.

       check_reverse_client_hostname_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              unverified reverse client hostname, and execute the  correspond-
              ing  action.   Note:  a result of "OK" is not allowed for safety
              reasons.  Instead, use DUNNO in order to exclude specific  hosts
              from  blacklists.   This feature is available in Postfix 2.7 and
              later.

       check_reverse_client_hostname_ns_access type:table
              Search the specified access(5) database for the DNS servers  for
              the  unverified  reverse client hostname, and execute the corre-
              sponding action.  Note: a result of  "OK"  is  not  allowed  for
              safety reasons.  Instead, use DUNNO in order to exclude specific
              hosts from blacklists.  This feature is available in Postfix 2.7
              and later.

       check_sasl_access type:table
              Use  the remote SMTP client SASL user name as lookup key for the
              specified access(5) database. The lookup key has the form "user-
              name@domainname"   when  the  smtpd_sasl_local_domain  parameter
              value is non-empty.   Unlike  the  check_client_access  feature,
              check_sasl_access  does not perform matches of parent domains or
              IP subnet ranges.  This feature is available with  Postfix  ver-
              sion 2.11 and later.

       permit_inet_interfaces
              Permit   the   request   when  the  client  IP  address  matches
              $inet_interfaces.

       permit_mynetworks
              Permit the request when the client IP address matches  any  net-
              work or network address listed in  $mynetworks.

       permit_sasl_authenticated
              Permit the request when the client is successfully authenticated
              via the RFC 4954 (AUTH) protocol.

       permit_tls_all_clientcerts
              Permit the request when the remote SMTP  client  certificate  is
              verified  successfully.  This option must be used only if a spe-
              cial CA issues the certificates and only this CA  is  listed  as
              trusted  CA.  Otherwise,  clients with a third-party certificate
              would also be allowed to relay.  Specify  "tls_append_default_CA
              =  no" when the trusted CA is specified with smtpd_tls_CAfile or
              smtpd_tls_CApath, to prevent Postfix  from  appending  the  sys-
              tem-supplied  default CAs.  This feature is available with Post-
              fix version 2.2.

       permit_tls_clientcerts
              Permit the request when the remote SMTP client certificate  fin-
              gerprint  or  public  key fingerprint (Postfix 2.9 and later) is
              listed in $relay_clientcerts.  The fingerprint digest  algorithm
              is  configurable  via the smtpd_tls_fingerprint_digest parameter
              (hard-coded as md5 prior to Postfix version 2.5).  This  feature
              is available with Postfix version 2.2.

       reject_rbl_client rbl_domain=d.d.d.d
              Reject  the  request when the reversed client network address is
              listed with the A record  "d.d.d.d"  under  rbl_domain  (Postfix
              version 2.1 and later only).  Each "d" is a number, or a pattern
              inside "[]" that contains one or more ";"-separated  numbers  or
              number..number  ranges  (Postfix  version 2.8 and later).  If no
              "=d.d.d.d" is specified, reject the request  when  the  reversed
              client  network  address  is  listed  with  any  A  record under
              rbl_domain.
              The maps_rbl_reject_code parameter specifies the  response  code
              for  rejected  requests  (default:   554), the default_rbl_reply
              parameter  specifies  the  default   server   reply,   and   the
              rbl_reply_maps   parameter  specifies tables with server replies
              indexed by rbl_domain.  This feature is available in Postfix 2.0
              and later.

       permit_dnswl_client dnswl_domain=d.d.d.d
              Accept  the  request when the reversed client network address is
              listed with the A record "d.d.d.d" under dnswl_domain.  Each "d"
              is  a number, or a pattern inside "[]" that contains one or more
              ";"-separated  numbers  or   number..number   ranges.    If   no
              "=d.d.d.d"  is  specified,  accept the request when the reversed
              client network  address  is  listed  with  any  A  record  under
              dnswl_domain.
              For  safety,  permit_dnswl_client  is  silently  ignored when it
              would  override  reject_unauth_destination.    The   result   is
              DEFER_IF_REJECT  when  whitelist  lookup fails.  This feature is
              available in Postfix 2.8 and later.

       reject_rhsbl_client rbl_domain=d.d.d.d
              Reject the request when the client hostname is listed with the A
              record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later
              only).  Each "d" is a number, or a pattern inside "[]" that con-
              tains one or more ";"-separated numbers or number..number ranges
              (Postfix version 2.8 and later).  If no "=d.d.d.d" is specified,
              reject the request when the client hostname is listed with any A
              record under rbl_domain. See the  reject_rbl_client  description
              above for additional RBL related configuration parameters.  This
              feature is available in Postfix 2.0 and later; with Postfix ver-
              sion  2.8  and  later,  reject_rhsbl_reverse_client will usually
              produce better results.

       permit_rhswl_client rhswl_domain=d.d.d.d
              Accept the request when the client hostname is listed with the A
              record "d.d.d.d" under rhswl_domain.  Each "d" is a number, or a
              pattern inside "[]" that contains one or more ";"-separated num-
              bers  or  number..number  ranges. If no "=d.d.d.d" is specified,
              accept the request when the client hostname is listed with any A
              record under rhswl_domain.
              Caution:  client  name whitelisting is fragile, since the client
              name lookup can fail due  to  temporary  outages.   Client  name
              whitelisting  should  be  used only to reduce false positives in
              e.g.  DNS-based blocklists,  and  not  for  making  access  rule
              exceptions.
              For  safety,  permit_rhswl_client  is  silently  ignored when it
              would  override  reject_unauth_destination.    The   result   is
              DEFER_IF_REJECT  when  whitelist  lookup fails.  This feature is
              available in Postfix 2.8 and later.

       reject_rhsbl_reverse_client rbl_domain=d.d.d.d
              Reject the request when the unverified reverse  client  hostname
              is  listed  with  the A record "d.d.d.d" under rbl_domain.  Each
              "d" is a number, or a pattern inside "[]" that contains  one  or
              more  ";"-separated  numbers  or  number..number  ranges.  If no
              "=d.d.d.d" is specified, reject the request when the  unverified
              reverse  client  hostname  is  listed  with  any  A record under
              rbl_domain. See  the  reject_rbl_client  description  above  for
              additional  RBL  related configuration parameters.  This feature
              is available in Postfix 2.8 and later.

       reject_unknown_client_hostname      (with      Postfix      <      2.3:
       reject_unknown_client)
              Reject the request when 1) the client IP  address->name  mapping
              fails,   2)   the   name->address   mapping  fails,  or  3)  the
              name->address mapping does not match the client IP address.
              This     is     a     stronger     restriction     than      the
              reject_unknown_reverse_client_hostname  feature,  which triggers
              only under condition 1) above.
              The unknown_client_reject_code parameter specifies the  response
              code  for  rejected requests (default: 450). The reply is always
              450 in case the address->name or name->address lookup failed due
              to a temporary problem.

       reject_unknown_reverse_client_hostname
              Reject   the   request   when  the  client  IP  address  has  no
              address->name mapping.
              This     is     a     weaker      restriction      than      the
              reject_unknown_client_hostname  feature, which requires not only
              that the address->name and  name->address  mappings  exist,  but
              also that the two mappings reproduce the client IP address.
              The  unknown_client_reject_code parameter specifies the response
              code for rejected requests (default: 450).  The reply is  always
              450  in  case the address->name lookup failed due to a temporary
              problem.
              This feature is available in Postfix 2.3 and later.

       In addition, you can use any of  the  following  generic  restrictions.
       These restrictions are applicable in any SMTP command context.

       check_policy_service servername
              Query  the  specified policy server. See the SMTPD_POLICY_README
              document for details. This feature is available in  Postfix  2.1
              and later.

       defer  Defer  the  request. The client is told to try again later. This
              restriction is useful at the end of a restriction list, to  make
              the default policy explicit.
              The  defer_code  parameter  specifies the SMTP server reply code
              (default: 450).

       defer_if_permit
              Defer the request if some later restriction would result  in  an
              explicit  or  implicit  PERMIT  action.   This  is useful when a
              blacklisting feature fails due to  a  temporary  problem.   This
              feature is available in Postfix version 2.1 and later.

       defer_if_reject
              Defer  the  request  if some later restriction would result in a
              REJECT action.  This is useful when a whitelisting feature fails
              due  to a temporary problem.  This feature is available in Post-
              fix version 2.1 and later.

       permit Permit the request. This restriction is useful at the end  of  a
              restriction list, to make the default policy explicit.

       reject_multi_recipient_bounce
              Reject the request when the envelope sender is the null address,
              and the message has multiple envelope recipients. This usage has
              rare  but  legitimate  applications:  under  certain conditions,
              multi-recipient  mail  that  was  posted  with  the  DSN  option
              NOTIFY=NEVER may be forwarded with the null sender address.
              Note:  this  restriction  can  only  work  reliably when used in
              smtpd_data_restrictions    or    smtpd_end_of_data_restrictions,
              because  the  total number of recipients is not known at an ear-
              lier stage of the SMTP conversation.  Use at the RCPT stage will
              only reject the second etc.  recipient.
              The  multi_recipient_bounce_reject_code  parameter specifies the
              response code for rejected requests (default:  550).  This  fea-
              ture is available in Postfix 2.1 and later.

       reject_plaintext_session
              Reject  the  request  when the connection is not encrypted. This
              restriction should not be used  before  the  client  has  had  a
              chance  to  negotiate  encryption with the AUTH or STARTTLS com-
              mands.
              The plaintext_reject_code parameter specifies the response  code
              for  rejected  requests (default:  450).  This feature is avail-
              able in Postfix 2.3 and later.

       reject_unauth_pipelining
              Reject the request when the client sends SMTP commands ahead  of
              time where it is not allowed, or when the client sends SMTP com-
              mands ahead of time without knowing that Postfix  actually  sup-
              ports  ESMTP  command pipelining. This stops mail from bulk mail
              software that improperly uses ESMTP command pipelining in  order
              to speed up deliveries.
              With  Postfix  2.6 and later, the SMTP server sets a per-session
              flag whenever it detects illegal pipelining, including pipelined
              HELO or EHLO commands. The reject_unauth_pipelining feature sim-
              ply tests whether the flag was set at any point in  time  during
              the session.
              With older Postfix versions, reject_unauth_pipelining checks the
              current status of the input read queue, and  its  usage  is  not
              recommended in contexts other than smtpd_data_restrictions.

       reject Reject  the  request. This restriction is useful at the end of a
              restriction list, to make  the  default  policy  explicit.   The
              reject_code  configuration parameter specifies the response code
              for rejected requests (default: 554).

       sleep seconds
              Pause for the specified number of seconds and proceed  with  the
              next  restriction in the list, if any. This may stop zombie mail
              when used as:
              /etc/postfix/main.cf:
                  smtpd_client_restrictions =
                      sleep 1, reject_unauth_pipelining
                  smtpd_delay_reject = no
              This feature is available in Postfix 2.3.

       warn_if_reject
              A safety net for testing. When "warn_if_reject" is placed before
              a  reject-type  restriction,  access  table query, or check_pol-
              icy_service query, this logs a "reject_warning" message  instead
              of rejecting a request (when a reject-type restriction fails due
              to a temporary error, this logs a "reject_warning"  message  for
              any  implicit "defer_if_permit" actions that would normally pre-
              vent mail from being accepted by some later access restriction).
              This feature has no effect on defer_if_reject restrictions.

       Other restrictions that are valid in this context:

             SMTP  command specific restrictions that are described under the
              smtpd_helo_restrictions,      smtpd_sender_restrictions       or
              smtpd_recipient_restrictions  parameters.  When  helo, sender or
              recipient restrictions are  listed  under  smtpd_client_restric-
              tions, they have effect only with "smtpd_delay_reject = yes", so
              that $smtpd_client_restrictions is evaluated at the time of  the
              RCPT TO command.

       Example:

       smtpd_client_restrictions = permit_mynetworks, reject_unknown_client_hostname

smtpd_command_filter (default: empty)
       A  mechanism to transform commands from remote SMTP clients.  This is a
       last-resort tool to work around client commands that  break  interoper-
       ability  with the Postfix SMTP server.  Other uses involve fault injec-
       tion to test Postfix's handling of invalid commands.

       Specify the name of a "type:table" lookup table. The search  string  is
       the  SMTP  command as received from the remote SMTP client, except that
       initial whitespace and the trailing <CR><LF> are removed.   The  result
       value is executed by the Postfix SMTP server.

       There is no need to use smtpd_command_filter for the following cases:

             Use "resolve_numeric_domain = yes" to accept "user@ipaddress".

             Postfix already accepts the correct form "user@[ipaddress]". Use
              virtual_alias_maps or canonical_maps  to  translate  these  into
              domain names if necessary.

             Use "strict_rfc821_envelopes = no" to accept "RCPT TO:<User Name
              <user@example.com>>". Postfix will ignore the "User  Name"  part
              and deliver to the <user@example.com> address.

       Examples  of  problems that can be solved with the smtpd_command_filter
       feature:

       /etc/postfix/main.cf:
           smtpd_command_filter = pcre:/etc/postfix/command_filter

       /etc/postfix/command_filter:
           # Work around clients that send malformed HELO commands.
           /^HELO\s*$/ HELO domain.invalid

           # Work around clients that send empty lines.
           /^\s*$/     NOOP

           # Work around clients that send RCPT TO:<'user@domain'>.
           # WARNING: do not lose the parameters that follow the address.
           /^(RCPT\s+TO:\s*<)'([^[:space:]]+)'(>.*)/     $1$2$3

           # Append XVERP to MAIL FROM commands to request VERP-style delivery.
           # See VERP_README for more information on how to use Postfix VERP.
           /^(MAIL FROM:\s*<listname@example\.com>.*)/   $1 XVERP

           # Bounce-never mail sink. Use notify_classes=bounce,resource,software
           # to send bounced mail to the postmaster (with message body removed).
           /^(RCPT\s+TO:\s*<.*>.*)\s+NOTIFY=\S+(.*)/     $1 NOTIFY=NEVER$2
           /^(RCPT\s+TO:.*)/                             $1 NOTIFY=NEVER

       This feature is available in Postfix 2.7.

smtpd_data_restrictions (default: empty)
       Optional access restrictions that the Postfix SMTP  server  applies  in
       the context of the SMTP DATA command.  See SMTPD_ACCESS_README, section
       "Delayed evaluation of SMTP access restriction lists" for a  discussion
       of evaluation context and time.

       This feature is available in Postfix 2.0 and later.

       Specify  a list of restrictions, separated by commas and/or whitespace.
       Continue  long  lines  by  starting  the  next  line  with  whitespace.
       Restrictions  are applied in the order as specified; the first restric-
       tion that matches wins.

       The following restrictions are valid in this context:

             Generic restrictions that can be used in any SMTP  command  con-
              text, described under smtpd_client_restrictions.

             SMTP    command    specific    restrictions    described   under
              smtpd_client_restrictions,              smtpd_helo_restrictions,
              smtpd_sender_restrictions or smtpd_recipient_restrictions.

             However,  no  recipient  information is available in the case of
              multi-recipient mail. Acting on only one recipient would be mis-
              leading,   because  any  decision  will  affect  all  recipients
              equally. Acting on all recipients would require a possibly  very
              large  amount  of  memory,  and would also be misleading for the
              reasons mentioned before.

       Examples:

       smtpd_data_restrictions = reject_unauth_pipelining
       smtpd_data_restrictions = reject_multi_recipient_bounce

smtpd_delay_open_until_valid_rcpt (default: yes)
       Postpone the start of an SMTP mail transaction until a  valid  RCPT  TO
       command  is received. Specify "no" to create a mail transaction as soon
       as the Postfix SMTP server receives a valid MAIL FROM command.

       With sites that reject lots of mail, the default  setting  reduces  the
       use  of  disk,  CPU and memory resources. The downside is that rejected
       recipients are logged with NOQUEUE instead of a  mail  transaction  ID.
       This complicates the logfile analysis of multi-recipient mail.

       This feature is available in Postfix 2.3 and later.

smtpd_delay_reject (default: yes)
       Wait until the RCPT TO command before evaluating $smtpd_client_restric-
       tions, $smtpd_helo_restrictions and $smtpd_sender_restrictions, or wait
       until the ETRN command before evaluating $smtpd_client_restrictions and
       $smtpd_helo_restrictions.

       This feature is turned on by default because  some  clients  apparently
       mis-behave  when  the  Postfix SMTP server rejects commands before RCPT
       TO.

       The default setting has one major benefit: it  allows  Postfix  to  log
       recipient  address  information when rejecting a client name/address or
       sender address, so that it is possible to find out whose mail is  being
       rejected.

smtpd_discard_ehlo_keyword_address_maps (default: empty)
       Lookup  tables,  indexed  by  the remote SMTP client address, with case
       insensitive lists of EHLO keywords (pipelining, starttls,  auth,  etc.)
       that  the  Postfix  SMTP server will not send in the EHLO response to a
       remote SMTP client. See smtpd_discard_ehlo_keywords for  details.   The
       tables are not searched by hostname for robustness reasons.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       This feature is available in Postfix 2.2 and later.

smtpd_discard_ehlo_keywords (default: empty)
       A  case  insensitive list of EHLO keywords (pipelining, starttls, auth,
       etc.) that the Postfix SMTP server will not send in the  EHLO  response
       to a remote SMTP client.

       This feature is available in Postfix 2.2 and later.

       Notes:

             Specify the silent-discard pseudo keyword to prevent this action
              from being logged.

             Use the smtpd_discard_ehlo_keyword_address_maps feature to  dis-
              card EHLO keywords selectively.

smtpd_dns_reply_filter (default: empty)
       Optional  filter  for  Postfix  SMTP  server  DNS  lookup results.  See
       smtp_dns_reply_filter for details including an example.

       This feature is available in Postfix 3.0 and later.

smtpd_end_of_data_restrictions (default: empty)
       Optional access restrictions that the Postfix SMTP  server  applies  in
       the  context of the SMTP END-OF-DATA command.  See SMTPD_ACCESS_README,
       section "Delayed evaluation of SMTP access  restriction  lists"  for  a
       discussion of evaluation context and time.

       This feature is available in Postfix 2.2 and later.

       See smtpd_data_restrictions for details and limitations.

smtpd_enforce_tls (default: no)
       Mandatory  TLS:  announce  STARTTLS support to remote SMTP clients, and
       require that clients use TLS encryption.  According to  RFC  2487  this
       MUST NOT be applied in case of a publicly-referenced SMTP server.  This
       option is therefore off by default.

       Note 1: "smtpd_enforce_tls = yes" implies "smtpd_tls_auth_only =  yes".

       Note  2:  when  invoked  via  "sendmail  -bs", Postfix will never offer
       STARTTLS due to insufficient privileges to access  the  server  private
       key. This is intended behavior.

       This  feature  is  available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtpd_tls_security_level instead.

smtpd_error_sleep_time (default: 1s)
       With Postfix version 2.1 and later:  the  SMTP  server  response  delay
       after  a  client has made more than $smtpd_soft_error_limit errors, and
       fewer than $smtpd_hard_error_limit errors, without delivering mail.

       With Postfix version 2.0 and earlier:  the  SMTP  server  delay  before
       sending  a reject (4xx or 5xx) response, when the client has made fewer
       than $smtpd_soft_error_limit errors without delivering mail.

smtpd_etrn_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the  con-
       text  of  a  client  ETRN  command.   See  SMTPD_ACCESS_README, section
       "Delayed evaluation of SMTP access restriction lists" for a  discussion
       of evaluation context and time.

       The Postfix ETRN implementation accepts only destinations that are eli-
       gible for the Postfix "fast flush" service. See  the  ETRN_README  file
       for details.

       Specify  a list of restrictions, separated by commas and/or whitespace.
       Continue  long  lines  by  starting  the  next  line  with  whitespace.
       Restrictions  are applied in the order as specified; the first restric-
       tion that matches wins.

       The following restrictions are specific to the domain name  information
       received with the ETRN command.

       check_etrn_access type:table
              Search the specified access database for the ETRN domain name or
              its parent domains. See the access(5) manual page for details.

       Other restrictions that are valid in this context:

             Generic restrictions that can be used in any SMTP  command  con-
              text, described under smtpd_client_restrictions.

             SMTP    command    specific    restrictions    described   under
              smtpd_client_restrictions and smtpd_helo_restrictions.

       Example:

       smtpd_etrn_restrictions = permit_mynetworks, reject

smtpd_expansion_filter (default: see postconf -d output)
       What characters are allowed in $name expansions of RBL reply templates.
       Characters  not  in  the  allowed  set are replaced by "_".  Use C like
       escapes to specify special characters such as whitespace.

       This parameter is not subjected to $parameter expansion.

       This feature is available in Postfix 2.0 and later.

smtpd_forbidden_commands (default: CONNECT, GET, POST)
       List of commands that cause the Postfix SMTP server to immediately ter-
       minate  the  session  with  a  221 code. This can be used to disconnect
       clients that obviously attempt to abuse the system. In addition to  the
       commands  listed  in  this parameter, commands that follow the "Label:"
       format of message headers will also cause a disconnect.

       This feature is available in Postfix 2.2 and later.

smtpd_hard_error_limit (default: normal: 20, overload: 1)
       The maximal number of errors a remote SMTP client is  allowed  to  make
       without  delivering  mail. The Postfix SMTP server disconnects when the
       limit is exceeded. Normally the default limit is  20,  but  it  changes
       under overload to just 1. With Postfix 2.5 and earlier, the SMTP server
       always allows up to 20 errors by default.

smtpd_helo_required (default: no)
       Require that a remote SMTP client introduces itself with  the  HELO  or
       EHLO  command  before  sending  the MAIL command or other commands that
       require EHLO negotiation.

       Example:

       smtpd_helo_required = yes

smtpd_helo_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the  con-
       text  of  a  client  HELO  command.   See  SMTPD_ACCESS_README, section
       "Delayed evaluation of SMTP access restriction lists" for a  discussion
       of evaluation context and time.

       The default is to permit everything.

       Note:  specify  "smtpd_helo_required  =  yes"  to  fully  enforce  this
       restriction (without "smtpd_helo_required = yes", a client  can  simply
       skip smtpd_helo_restrictions by not sending HELO or EHLO).

       Specify  a list of restrictions, separated by commas and/or whitespace.
       Continue  long  lines  by  starting  the  next  line  with  whitespace.
       Restrictions  are applied in the order as specified; the first restric-
       tion that matches wins.

       The following restrictions are specific  to  the  hostname  information
       received with the HELO or EHLO command.

       check_helo_access type:table
              Search  the  specified  access(5)  database for the HELO or EHLO
              hostname  or  parent  domains,  and  execute  the  corresponding
              action.   Note:  specify  "smtpd_helo_required  =  yes" to fully
              enforce this restriction (without "smtpd_helo_required = yes", a
              client  can simply skip check_helo_access by not sending HELO or
              EHLO).

       check_helo_a_access type:table
              Search the specified access(5) database for the IP addresses for
              the HELO or EHLO hostname, and execute the corresponding action.
              Note 1: a result of "OK" is  not  allowed  for  safety  reasons.
              Instead,  use  DUNNO  in  order  to  exclude specific hosts from
              blacklists.  Note 2:  specify  "smtpd_helo_required  =  yes"  to
              fully  enforce  this restriction (without "smtpd_helo_required =
              yes", a client can simply skip check_helo_a_access by not  send-
              ing HELO or EHLO).  This feature is available in Postfix 3.0 and
              later.

       check_helo_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              HELO  or  EHLO  hostname,  and execute the corresponding action.
              Note 1: a result of "OK" is  not  allowed  for  safety  reasons.
              Instead,  use  DUNNO  in  order  to  exclude specific hosts from
              blacklists.  Note 2:  specify  "smtpd_helo_required  =  yes"  to
              fully  enforce  this restriction (without "smtpd_helo_required =
              yes", a client can simply skip check_helo_mx_access by not send-
              ing HELO or EHLO).  This feature is available in Postfix 2.1 and
              later.

       check_helo_ns_access type:table
              Search the specified access(5) database for the DNS servers  for
              the HELO or EHLO hostname, and execute the corresponding action.
              Note 1: a result of "OK" is  not  allowed  for  safety  reasons.
              Instead,  use  DUNNO  in  order  to  exclude specific hosts from
              blacklists.  Note 2:  specify  "smtpd_helo_required  =  yes"  to
              fully  enforce  this restriction (without "smtpd_helo_required =
              yes", a client can simply skip check_helo_ns_access by not send-
              ing  HELO or EHLO). This feature is available in Postfix 2.1 and
              later.

       reject_invalid_helo_hostname (with Postfix < 2.3:  reject_invalid_host-
       name)
              Reject the request when the HELO or EHLO hostname is  malformed.
              Note:  specify "smtpd_helo_required = yes" to fully enforce this
              restriction (without "smtpd_helo_required = yes", a  client  can
              simply  skip reject_invalid_helo_hostname by not sending HELO or
              EHLO).
              The invalid_hostname_reject_code specifies the response code for
              rejected requests (default: 501).

       reject_non_fqdn_helo_hostname       (with      Postfix      <      2.3:
       reject_non_fqdn_hostname)
              Reject  the  request  when  the  HELO or EHLO hostname is not in
              fully-qualified domain or address literal form, as  required  by
              the  RFC.  Note:  specify  "smtpd_helo_required  = yes" to fully
              enforce this restriction (without "smtpd_helo_required = yes", a
              client  can  simply  skip  reject_non_fqdn_helo_hostname  by not
              sending HELO or EHLO).
              The non_fqdn_reject_code parameter specifies the  response  code
              for rejected requests (default: 504).

       reject_rhsbl_helo rbl_domain=d.d.d.d
              Reject the request when the HELO or EHLO hostname is listed with
              the A record "d.d.d.d" under rbl_domain (Postfix version 2.1 and
              later  only).   Each  "d"  is a number, or a pattern inside "[]"
              that contains one or more ";"-separated numbers or  number..num-
              ber ranges (Postfix version 2.8 and later).  If no "=d.d.d.d" is
              specified, reject the request when the HELO or EHLO hostname  is
              listed   with   any   A   record   under   rbl_domain.  See  the
              reject_rbl_client description for additional RBL related config-
              uration  parameters.   Note: specify "smtpd_helo_required = yes"
              to fully enforce this restriction (without  "smtpd_helo_required
              =  yes", a client can simply skip reject_rhsbl_helo by not send-
              ing HELO or EHLO). This feature is available in Postfix 2.0  and
              later.

       reject_unknown_helo_hostname  (with Postfix < 2.3: reject_unknown_host-
       name)
              Reject  the  request when the HELO or EHLO hostname has no DNS A
              or MX record.
              The reply is  specified  with  the  unknown_hostname_reject_code
              parameter    (default:   450)   or   unknown_helo_hostname_temp-
              fail_action  (default:  defer_if_permit).   See  the  respective
              parameter descriptions for details.
              Note:  specify "smtpd_helo_required = yes" to fully enforce this
              restriction (without "smtpd_helo_required = yes", a  client  can
              simply  skip reject_unknown_helo_hostname by not sending HELO or
              EHLO).

       Other restrictions that are valid in this context:

             Generic restrictions that can be used in any SMTP  command  con-
              text, described under smtpd_client_restrictions.

             Client   hostname   or  network  address  specific  restrictions
              described under smtpd_client_restrictions.

             SMTP   command    specific    restrictions    described    under
              smtpd_sender_restrictions or smtpd_recipient_restrictions.  When
              sender   or   recipient   restrictions    are    listed    under
              smtpd_helo_restrictions,    they    have    effect   only   with
              "smtpd_delay_reject = yes", so that $smtpd_helo_restrictions  is
              evaluated at the time of the RCPT TO command.

       Examples:

       smtpd_helo_restrictions = permit_mynetworks, reject_invalid_helo_hostname
       smtpd_helo_restrictions = permit_mynetworks, reject_unknown_helo_hostname

smtpd_history_flush_threshold (default: 100)
       The  maximal number of lines in the Postfix SMTP server command history
       before it is flushed upon receipt of EHLO, RSET, or end of DATA.

smtpd_junk_command_limit (default: normal: 100, overload: 1)
       The number of junk commands (NOOP, VRFY, ETRN or RSET)  that  a  remote
       SMTP client can send before the Postfix SMTP server starts to increment
       the error counter with each junk command.  The junk  command  count  is
       reset after mail is delivered.  See also the smtpd_error_sleep_time and
       smtpd_soft_error_limit configuration parameters.  Normally the  default
       limit is 100, but it changes under overload to just 1. With Postfix 2.5
       and earlier, the SMTP server always allows up to 100 junk  commands  by
       default.

smtpd_log_access_permit_actions (default: empty)
       Enable  logging  of  the  named  "permit" actions in SMTP server access
       lists (by default, the SMTP server logs "reject" actions but not  "per-
       mit"  actions).   This feature does not affect conditional actions such
       as "defer_if_permit".

       Specify a list of "permit" action names, "/file/name"  or  "type:table"
       patterns,  separated  by  commas and/or whitespace. The list is matched
       left to right, and the search stops on the first match. A  "/file/name"
       pattern  is  replaced  by  its contents; a "type:table" lookup table is
       matched when a  name  matches  a  lookup  key  (the  lookup  result  is
       ignored).   Continue  long  lines by starting the next line with white-
       space. Specify "!pattern" to exclude a name from the list.

       Examples:

       /etc/postfix/main.cf:
           # Log all "permit" actions.
           smtpd_log_access_permit_actions = static:all

       /etc/postfix/main.cf:
           # Log "permit_dnswl_client" only.
           smtpd_log_access_permit_actions = permit_dnswl_client

       This feature is available in Postfix 2.10 and later.

smtpd_milters (default: empty)
       A list of Milter (mail filter) applications for new mail  that  arrives
       via  the  Postfix smtpd(8) server. Specify space or comma as separator.
       See the MILTER_README document for details.

       This feature is available in Postfix 2.3 and later.

smtpd_noop_commands (default: empty)
       List of commands that the Postfix SMTP server replies to with "250 Ok",
       without  doing any syntax checks and without changing state.  This list
       overrides any commands built into the Postfix SMTP server.

smtpd_null_access_lookup_key (default: <>)
       The lookup key to be used in SMTP access(5) tables instead of the  null
       sender address.

smtpd_peername_lookup (default: yes)
       Attempt to look up the remote SMTP client hostname, and verify that the
       name matches the client IP address. A client name is set  to  "unknown"
       when  it  cannot  be looked up or verified, or when name lookup is dis-
       abled.  Turning off name lookup reduces delays due to  DNS  lookup  and
       increases the maximal inbound delivery rate.

       This feature is available in Postfix 2.3 and later.

smtpd_per_record_deadline (default: normal: no, overload: yes)
       Change  the  behavior  of  the smtpd_timeout and smtpd_starttls_timeout
       time limits, from a time limit per read or write system call, to a time
       limit  to send or receive a complete record (an SMTP command line, SMTP
       response line, SMTP message content line,  or  TLS  protocol  message).
       This limits the impact from hostile peers that trickle data one byte at
       a time.

       Note: when per-record deadlines are enabled, a short timeout may  cause
       problems  with TLS over very slow network connections.  The reasons are
       that a TLS protocol message can be up to 16 kbytes long  (with  TLSv1),
       and that an entire TLS protocol message must be sent or received within
       the per-record deadline.

       This feature is available in Postfix 2.9 and later. With older  Postfix
       releases, the behavior is as if this parameter is set to "no".

smtpd_policy_service_default_action  (default:  451 4.3.5 Server configuration
       problem)
       The default action when an SMTPD policy service request fails.  Specify
       "DUNNO"  to  behave  as if the failed  SMTPD policy service request was
       not sent, and to continue processing other access restrictions, if any.

       Limitations:

             This parameter may specify any value that would be a valid SMTPD
              policy server response (or access(5)  map  lookup  result).   An
              access(5)  map or policy server in this parameter value may need
              to be declared in advance with a restriction_class setting.

             If the specified  action  invokes  another  check_policy_service
              request, that request will have the built-in default action.

       This feature is available in Postfix 3.0 and later.

smtpd_policy_service_max_idle (default: 300s)
       The time after which an idle SMTPD policy service connection is closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_max_ttl (default: 1000s)
       The time after which an  active  SMTPD  policy  service  connection  is
       closed.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_policy_context (default: empty)
       Optional  information  that  the  Postfix  SMTP server specifies in the
       "policy_context" attribute of a policy service request (originally,  to
       share  the  same  service  endpoint among multiple check_policy_service
       clients).

       This feature is available in Postfix 3.1 and later.

smtpd_policy_service_request_limit (default: 0)
       The maximal number of requests per SMTPD policy service connection,  or
       zero  (no  limit). Once a connection reaches this limit, the connection
       is closed and the next request will be sent over a new connection. This
       is a workaround to avoid error-recovery delays with policy servers that
       cannot maintain a persistent connection.

       This feature is available in Postfix 3.0 and later.

smtpd_policy_service_retry_delay (default: 1s)
       The delay between attempts to resend  a  failed  SMTPD  policy  service
       request. Specify a value greater than zero.

       This feature is available in Postfix 3.0 and later.

smtpd_policy_service_timeout (default: 100s)
       The time limit for connecting to, writing to, or receiving from a dele-
       gated SMTPD policy server.

       This feature is available in Postfix 2.1 and later.

smtpd_policy_service_try_limit (default: 2)
       The maximal number of attempts to send an SMTPD policy service  request
       before giving up. Specify a value greater than zero.

       This feature is available in Postfix 3.0 and later.

smtpd_proxy_ehlo (default: $myhostname)
       How  the  Postfix SMTP server announces itself to the proxy filter.  By
       default, the Postfix hostname is used.

       This feature is available in Postfix 2.1 and later.

smtpd_proxy_filter (default: empty)
       The hostname and TCP port of the  mail  filtering  proxy  server.   The
       proxy  receives  all mail from the Postfix SMTP server, and is supposed
       to give the result to another Postfix SMTP server process.

       Specify  "host:port"  or  "inet:host:port"  for  a  TCP  endpoint,   or
       "unix:pathname"  for  a UNIX-domain endpoint. The host can be specified
       as an IP address or as a symbolic name; no MX lookups are  done.   When
       no  "host"  or  "host:"   are  specified, the local machine is assumed.
       Pathname interpretation is relative to the Postfix queue directory.

       This feature is available in Postfix 2.1 and later.

       The "inet:" and "unix:" prefixes  are  available  in  Postfix  2.3  and
       later.

smtpd_proxy_options (default: empty)
       List  of  options that control how the Postfix SMTP server communicates
       with a before-queue content filter. Specify zero or more of the follow-
       ing, separated by comma or whitespace.

       speed_adjust
              Do  not connect to a before-queue content filter until an entire
              message has been received. This reduces the number of simultane-
              ous before-queue content filter processes.

       NOTE   1:  A  filter  must  not  selectively  reject  recipients  of  a
       multi-recipient message.  Rejecting all recipients is OK, as is accept-
       ing all recipients.

       NOTE  2:  This feature increases the minimum amount of free queue space
       by $message_size_limit. The extra space is needed to save  the  message
       to a temporary file.

       This feature is available in Postfix 2.7 and later.

smtpd_proxy_timeout (default: 100s)
       The  time  limit  for  connecting  to a proxy filter and for sending or
       receiving information.  When a  connection  fails  the  client  gets  a
       generic  error message while more detailed information is logged to the
       maillog file.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

       This feature is available in Postfix 2.1 and later.

smtpd_recipient_limit (default: 1000)
       The  maximal  number of recipients that the Postfix SMTP server accepts
       per message delivery request.

smtpd_recipient_overshoot_limit (default: 1000)
       The number of recipients that a remote SMTP client can send  in  excess
       of  the limit specified with $smtpd_recipient_limit, before the Postfix
       SMTP server increments the per-session  error  count  for  each  excess
       recipient.

smtpd_recipient_restrictions (default: see postconf -d output)
       Optional  restrictions that the Postfix SMTP server applies in the con-
       text of a client RCPT TO command, after smtpd_relay_restrictions.   See
       SMTPD_ACCESS_README,   section   "Delayed  evaluation  of  SMTP  access
       restriction lists" for a discussion of evaluation context and time.

       With Postfix versions before 2.10, the rules for relay  permission  and
       spam blocking were combined under smtpd_recipient_restrictions, result-
       ing in error-prone configuration.  As of Postfix 2.10, relay permission
       rules are preferably implemented with smtpd_relay_restrictions, so that
       a permissive spam blocking  policy  under  smtpd_recipient_restrictions
       will no longer result in a permissive mail relay policy.

       For  backwards  compatibility, sites that migrate from Postfix versions
       before 2.10 can set smtpd_relay_restrictions to the  empty  value,  and
       use smtpd_recipient_restrictions exactly as before.

       IMPORTANT:  Either  the  smtpd_relay_restrictions  or the smtpd_recipi-
       ent_restrictions parameter must specify at least one of  the  following
       restrictions. Otherwise Postfix will refuse to receive mail:

           reject, reject_unauth_destination

           defer, defer_if_permit, defer_unauth_destination

       Specify  a list of restrictions, separated by commas and/or whitespace.
       Continue  long  lines  by  starting  the  next  line  with  whitespace.
       Restrictions  are applied in the order as specified; the first restric-
       tion that matches wins.

       The following restrictions are specific to the recipient  address  that
       is received with the RCPT TO command.

       check_recipient_access type:table
              Search the specified access(5) database for the resolved RCPT TO
              address, domain, parent domains, or localpart@, and execute  the
              corresponding action.

       check_recipient_a_access type:table
              Search the specified access(5) database for the IP addresses for
              the RCPT TO domain, and execute the corresponding action.  Note:
              a result of "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.   This
              feature is available in Postfix 3.0 and later.

       check_recipient_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              RCPT TO domain, and execute the corresponding action.   Note:  a
              result  of  "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.   This
              feature is available in Postfix 2.1 and later.

       check_recipient_ns_access type:table
              Search  the specified access(5) database for the DNS servers for
              the RCPT TO domain, and execute the corresponding action.  Note:
              a result of "OK" is not allowed for safety reasons. Instead, use
              DUNNO in order to exclude specific hosts from blacklists.   This
              feature is available in Postfix 2.1 and later.

       permit_auth_destination
              Permit the request when one of the following is true:

             Postfix  is  mail forwarder: the resolved RCPT TO domain matches
              $relay_domains or a subdomain thereof, and the address  contains
              no sender-specified routing (user@elsewhere@domain),

             Postfix  is  the  final destination: the resolved RCPT TO domain
              matches  $mydestination,  $inet_interfaces,   $proxy_interfaces,
              $virtual_alias_domains,  or  $virtual_mailbox_domains,  and  the
              address  contains  no   sender-specified   routing   (user@else-
              where@domain).

       permit_mx_backup
              Permit  the  request when the local mail system is backup MX for
              the RCPT TO domain, or when the domain is an authorized destina-
              tion (see permit_auth_destination for definition).

             Safety:  permit_mx_backup  does  not  accept addresses that have
              sender-specified  routing   information   (example:   user@else-
              where@domain).

             Safety:  permit_mx_backup  can  be  vulnerable  to  mis-use when
              access is not restricted with permit_mx_backup_networks.

             Safety: as of Postfix version 2.3,  permit_mx_backup  no  longer
              accepts the address when the local mail system is primary MX for
              the recipient domain.  Exception: permit_mx_backup  accepts  the
              address  when  it  specifies an authorized destination (see per-
              mit_auth_destination for definition).

             Limitation: mail may be rejected in  case  of  a  temporary  DNS
              lookup problem with Postfix prior to version 2.0.

       reject_non_fqdn_recipient
              Reject   the  request  when  the  RCPT  TO  address  is  not  in
              fully-qualified domain form, as required by the RFC.
              The non_fqdn_reject_code parameter specifies the  response  code
              for rejected requests (default: 504).

       reject_rhsbl_recipient rbl_domain=d.d.d.d
              Reject  the request when the RCPT TO domain is listed with the A
              record "d.d.d.d" under rbl_domain (Postfix version 2.1 and later
              only).  Each "d" is a number, or a pattern inside "[]" that con-
              tains one or more ";"-separated numbers or number..number ranges
              (Postfix  version 2.8 and later). If no "=d.d.d.d" is specified,
              reject the request when the RCPT TO domain is listed with any  A
              record under rbl_domain.
              The  maps_rbl_reject_code  parameter specifies the response code
              for rejected  requests  (default:  554);  the  default_rbl_reply
              parameter   specifies   the   default   server  reply;  and  the
              rbl_reply_maps parameter specifies tables  with  server  replies
              indexed  by  rbl_domain.   This  feature is available in Postfix
              version 2.0 and later.

       reject_unauth_destination
              Reject the request unless one of the following is true:

             Postfix is mail forwarder: the resolved RCPT TO  domain  matches
              $relay_domains   or   a   subdomain  thereof,  and  contains  no
              sender-specified routing (user@elsewhere@domain),

             Postfix is the final destination: the resolved  RCPT  TO  domain
              matches   $mydestination,  $inet_interfaces,  $proxy_interfaces,
              $virtual_alias_domains, or  $virtual_mailbox_domains,  and  con-
              tains no sender-specified routing (user@elsewhere@domain).
              The  relay_domains_reject_code  parameter specifies the response
              code for rejected requests (default: 554).

       defer_unauth_destination
              Reject the same requests as  reject_unauth_destination,  with  a
              non-permanent  error code.  This feature is available in Postfix
              2.10 and later.

       reject_unknown_recipient_domain
              Reject the request when Postfix is not final destination for the
              recipient domain, and the RCPT TO domain has 1) no DNS MX and no
              DNS A record or 2) a malformed MX record such as a record with a
              zero-length MX hostname (Postfix version 2.3 and later).
              The  reply  is  specified  with  the unknown_address_reject_code
              parameter   (default:   450),    unknown_address_tempfail_action
              (default:  defer_if_permit),  or  556  (nullmx,  Postfix 3.0 and
              later). See the respective parameter descriptions for details.

       reject_unlisted_recipient  (with  Postfix  version  2.0:  check_recipi-
       ent_maps)
              Reject the request when the RCPT TO address is not listed in the
              list   of  valid  recipients  for  its  domain  class.  See  the
              smtpd_reject_unlisted_recipient   parameter   description    for
              details.  This feature is available in Postfix 2.1 and later.

       reject_unverified_recipient
              Reject  the request when mail to the RCPT TO address is known to
              bounce, or when the recipient address destination is not  reach-
              able.   Address  verification information is managed by the ver-
              ify(8) server;  see  the  ADDRESS_VERIFICATION_README  file  for
              details.
              The  unverified_recipient_reject_code  parameter  specifies  the
              numerical response code when  an  address  is  known  to  bounce
              (default: 450, change into 550 when you are confident that it is
              safe to do so).
              The  unverified_recipient_defer_code  parameter  specifies   the
              numerical  response  code  when an address probe failed due to a
              temporary problem (default: 450).
              The unverified_recipient_tempfail_action parameter specifies the
              action  after  address  probe failure due to a temporary problem
              (default: defer_if_permit).
              This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

             Generic restrictions that can be used in any SMTP  command  con-
              text, described under smtpd_client_restrictions.

             SMTP    command    specific    restrictions    described   under
              smtpd_client_restrictions,      smtpd_helo_restrictions      and
              smtpd_sender_restrictions.

       Example:

       # The Postfix before 2.10 default mail relay policy. Later Postfix
       # versions implement this preferably with smtpd_relay_restrictions.
       smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

smtpd_reject_footer (default: empty)
       Optional  information  that  is appended after each Postfix SMTP server
       4XX or 5XX response.

       The following example uses "\c" at the start of the template (supported
       in Postfix 2.10 and later) to suppress the line break between the reply
       text and the footer text. With earlier  Postfix  versions,  the  footer
       text always begins on a new line, and the "\c" is output literally.

       /etc/postfix/main.cf:
           smtpd_reject_footer = \c. For assistance, call 800-555-0101.
            Please provide the following information in your problem report:
            time ($localtime), client ($client_address) and server
            ($server_name).

       Server response:

           550-5.5.1 <user@example> Recipient address rejected: User
           unknown. For assistance, call 800-555-0101. Please provide the
           following information in your problem report: time (Jan 4 15:42:00),
           client (192.168.1.248) and server (mail1.example.com).

       Note:  the  above  text  is meant to make it easier to find the Postfix
       logfile records for a failed SMTP  session.  The  text  itself  is  not
       logged to the Postfix SMTP server's maillog file.

       Be  sure  to keep the text as short as possible. Long text may be trun-
       cated before it is logged to the remote SMTP client's maillog file,  or
       before  it is returned to the sender in a delivery status notification.

       This feature supports a limited  number  of  $name  attributes  in  the
       footer  text.  These  are  replaced by their current value for the SMTP
       session:

       client_address
              The Client IP address that is logged in the maillog file.

       client_port
              The client TCP port that is logged in the maillog file.

       localtime
              The server local time (Mmm dd hh:mm:ss) that is  logged  in  the
              maillog file.

       server_name
              The server's myhostname value.  This attribute is made available
              for sites with multiple MTAs (perhaps behind  a  load-balancer),
              where  the  server  name  can  help  the  server support team to
              quickly find the right log files.

       Notes:

             NOT SUPPORTED are other attributes such as sender, recipient, or
              main.cf parameters.

             For  safety  reasons,  text  that  does  not match $smtpd_expan-
              sion_filter is censored.

       This feature supports the two-character sequence \n as a request for  a
       line break in the footer text. Postfix automatically inserts after each
       line break the three-digit SMTP reply code (and optional enhanced  sta-
       tus code) from the original Postfix reject message.

       To work around mail software that mis-handles multi-line replies, spec-
       ify the two-character sequence \c at the start of the  template.   This
       suppresses  the  line  break between the reply text and the footer text
       (Postfix 2.10 and later).

       This feature is available in Postfix 2.8 and later.

smtpd_reject_unlisted_recipient (default: yes)
       Request that the Postfix SMTP server rejects mail for unknown recipient
       addresses,  even  when  no  explicit  reject_unlisted_recipient  access
       restriction is specified. This prevents the Postfix queue from  filling
       up with undeliverable MAILER-DAEMON messages.

       An  address  is  always considered "known" when it matches a virtual(5)
       alias or a canonical(5) mapping.

             The recipient domain matches $mydestination, $inet_interfaces or
              $proxy_interfaces,   but   the   recipient   is  not  listed  in
              $local_recipient_maps, and $local_recipient_maps is not null.

             The recipient  domain  matches  $virtual_alias_domains  but  the
              recipient is not listed in $virtual_alias_maps.

             The  recipient  domain  matches $virtual_mailbox_domains but the
              recipient is not  listed  in  $virtual_mailbox_maps,  and  $vir-
              tual_mailbox_maps is not null.

             The recipient domain matches $relay_domains but the recipient is
              not listed in $relay_recipient_maps,  and  $relay_recipient_maps
              is not null.

       This feature is available in Postfix 2.1 and later.

smtpd_reject_unlisted_sender (default: no)
       Request  that  the Postfix SMTP server rejects mail from unknown sender
       addresses, even when no explicit reject_unlisted_sender access restric-
       tion  is specified. This can slow down an explosion of forged mail from
       worms or viruses.

       An address is always considered "known" when it  matches  a  virtual(5)
       alias or a canonical(5) mapping.

             The  sender  domain  matches $mydestination, $inet_interfaces or
              $proxy_interfaces, but the sender is not listed in $local_recip-
              ient_maps, and $local_recipient_maps is not null.

             The  sender domain matches $virtual_alias_domains but the sender
              is not listed in $virtual_alias_maps.

             The  sender  domain  matches  $virtual_mailbox_domains  but  the
              sender   is  not  listed  in  $virtual_mailbox_maps,  and  $vir-
              tual_mailbox_maps is not null.

             The sender domain matches $relay_domains but the sender  is  not
              listed  in  $relay_recipient_maps,  and $relay_recipient_maps is
              not null.

       This feature is available in Postfix 2.1 and later.

smtpd_relay_restrictions  (default:  permit_mynetworks,  permit_sasl_authenti-
       cated, defer_unauth_destination)
       Access restrictions for mail relay control that the Postfix SMTP server
       applies in the context of the RCPT  TO  command,  before  smtpd_recipi-
       ent_restrictions.  See SMTPD_ACCESS_README, section "Delayed evaluation
       of SMTP access restriction lists" for a discussion of  evaluation  con-
       text and time.

       With  Postfix  versions before 2.10, the rules for relay permission and
       spam blocking were combined under smtpd_recipient_restrictions, result-
       ing in error-prone configuration.  As of Postfix 2.10, relay permission
       rules are preferably implemented with smtpd_relay_restrictions, so that
       a  permissive  spam  blocking policy under smtpd_recipient_restrictions
       will no longer result in a permissive mail relay policy.

       For backwards compatibility, sites that migrate from  Postfix  versions
       before  2.10  can  set smtpd_relay_restrictions to the empty value, and
       use smtpd_recipient_restrictions exactly as before.

       By default, the Postfix SMTP server accepts:

             Mail from clients whose IP address matches $mynetworks, or:

             Mail to remote destinations that  match  $relay_domains,  except
              for  addresses that contain sender-specified routing (user@else-
              where@domain), or:

             Mail  to  local  destinations  that  match  $inet_interfaces  or
              $proxy_interfaces,  $mydestination,  $virtual_alias_domains,  or
              $virtual_mailbox_domains.

       IMPORTANT: Either the  smtpd_relay_restrictions  or  the  smtpd_recipi-
       ent_restrictions  parameter  must specify at least one of the following
       restrictions. Otherwise Postfix will refuse to receive mail:

           reject, reject_unauth_destination

           defer, defer_if_permit, defer_unauth_destination

       Specify a list of restrictions, separated by commas and/or  whitespace.
       Continue  long  lines  by  starting the next line with whitespace.  The
       same restrictions  are  available  as  documented  under  smtpd_recipi-
       ent_restrictions.

       This feature is available in Postix 2.10 and later.

smtpd_restriction_classes (default: empty)
       User-defined aliases for groups of access restrictions. The aliases can
       be  specified  in  smtpd_recipient_restrictions  etc.,   and   on   the
       right-hand side of a Postfix access(5) table.

       One  major  application  is for implementing per-recipient UCE control.
       See the RESTRICTION_CLASS_README document for other examples.

smtpd_sasl_application_name (default: smtpd)
       The application name that the Postfix SMTP server uses for SASL  server
       initialization.  This controls the name of the SASL configuration file.
       The default value is smtpd, corresponding to a SASL configuration  file
       named smtpd.conf.

       This  feature  is available in Postfix 2.1 and 2.2. With Postfix 2.3 it
       was renamed to smtpd_sasl_path.

smtpd_sasl_auth_enable (default: no)
       Enable SASL authentication in the Postfix SMTP server. By default,  the
       Postfix SMTP server does not use authentication.

       If a remote SMTP client is authenticated, the permit_sasl_authenticated
       access restriction can be used to permit relay access, like this:

           # With Postfix 2.10 and later, the mail relay policy is
           # preferably specified under smtpd_relay_restrictions.
           smtpd_relay_restrictions =
               permit_mynetworks, permit_sasl_authenticated, ...

       # With Postfix before 2.10, the relay policy can be
       # specified only under smtpd_recipient_restrictions.
       smtpd_recipient_restrictions =
           permit_mynetworks, permit_sasl_authenticated, ...

       To reject all SMTP connections from  unauthenticated  clients,  specify
       "smtpd_delay_reject = yes" (which is the default) and use:

           smtpd_client_restrictions = permit_sasl_authenticated, reject

       See  the SASL_README file for SASL configuration and operation details.

smtpd_sasl_authenticated_header (default: no)
       Report the SASL authenticated user name in the smtpd(8)  Received  mes-
       sage header.

       This feature is available in Postfix 2.3 and later.

smtpd_sasl_exceptions_networks (default: empty)
       What  remote  SMTP  clients the Postfix SMTP server will not offer AUTH
       support to.

       Some clients (Netscape 4 at least) have  a  bug  that  causes  them  to
       require  a  login  and  password whenever AUTH is offered, whether it's
       necessary or not. To work around this, specify,  for  example,  $mynet-
       works to prevent Postfix from offering AUTH to local clients.

       Specify  a list of network/netmask patterns, separated by commas and/or
       whitespace. The mask specifies the number of bits in the  network  part
       of  a host address. You can also "/file/name" or "type:table" patterns.
       A "/file/name" pattern is replaced  by  its  contents;  a  "type:table"
       lookup table is matched when a table entry matches a lookup string (the
       lookup result is ignored).  Continue long lines by  starting  the  next
       line  with whitespace. Specify "!pattern" to exclude an address or net-
       work block from the list.  The form "!/file/name" is supported only  in
       Postfix version 2.4 and later.

       Note:  IP  version 6 address information must be specified inside [] in
       the smtpd_sasl_exceptions_networks value, and in files  specified  with
       "/file/name".   IP  version  6 addresses contain the ":" character, and
       would otherwise be confused with a "type:table" pattern.

       Example:

       smtpd_sasl_exceptions_networks = $mynetworks

       This feature is available in Postfix 2.1 and later.

smtpd_sasl_local_domain (default: empty)
       The name of the Postfix SMTP server's local SASL authentication  realm.

       By default, the local authentication realm name is the null string.

       Examples:

       smtpd_sasl_local_domain = $mydomain
       smtpd_sasl_local_domain = $myhostname

smtpd_sasl_path (default: smtpd)
       Implementation-specific information that the Postfix SMTP server passes
       through to the  SASL  plug-in  implementation  that  is  selected  with
       smtpd_sasl_type.   Typically this specifies the name of a configuration
       file or rendezvous point.

       This feature is available in Postfix 2.3 and later. In earlier releases
       it was called smtpd_sasl_application_name.

smtpd_sasl_security_options (default: noanonymous)
       Postfix  SMTP  server SASL security options; as of Postfix 2.3 the list
       of available features depends on the SASL server implementation that is
       selected with smtpd_sasl_type.

       The  following  security features are defined for the cyrus server SASL
       implementation:

       Restrict what authentication mechanisms the Postfix  SMTP  server  will
       offer  to  the client.  The list of available authentication mechanisms
       is system dependent.

       Specify zero or more of the following:

       noplaintext
              Disallow methods that use plaintext passwords.

       noactive
              Disallow methods subject to active (non-dictionary) attack.

       nodictionary
              Disallow methods subject to passive (dictionary) attack.

       noanonymous
              Disallow methods that allow anonymous authentication.

       forward_secrecy
              Only allow methods that support forward secrecy (Dovecot  only).

       mutual_auth
              Only  allow  methods  that  provide  mutual  authentication (not
              available with Cyrus SASL version 1).

       By default, the Postfix SMTP server accepts plaintext passwords but not
       anonymous logins.

       Warning:  it  appears  that  clients  try authentication methods in the
       order as advertised by the  server  (e.g.,  PLAIN  ANONYMOUS  CRAM-MD5)
       which  means  that if you disable plaintext passwords, clients will log
       in anonymously, even when they should be able to use CRAM-MD5.  So,  if
       you  disable  plaintext  logins, disable anonymous logins too.  Postfix
       treats anonymous login as no authentication.

       Example:

       smtpd_sasl_security_options = noanonymous, noplaintext

smtpd_sasl_service (default: smtp)
       The service name that is passed to the SASL plug-in  that  is  selected
       with smtpd_sasl_type and smtpd_sasl_path.

       This  feature  is  available  in Postfix 2.11 and later. Prior versions
       behave as if "smtp" is specified.

smtpd_sasl_tls_security_options (default: $smtpd_sasl_security_options)
       The SASL authentication security options that the Postfix  SMTP  server
       uses for TLS encrypted SMTP sessions.

       This feature is available in Postfix 2.2 and later.

smtpd_sasl_type (default: cyrus)
       The  SASL  plug-in  type  that  the  Postfix SMTP server should use for
       authentication. The available types are listed with the  "postconf  -a"
       command.

       This feature is available in Postfix 2.3 and later.

smtpd_sender_login_maps (default: empty)
       Optional  lookup  table  with  the SASL login names that own the sender
       (MAIL FROM) addresses.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.  With lookups from indexed files such as DB or DBM,  or  from
       networked  tables such as NIS, LDAP or SQL, the following search opera-
       tions are done with a sender address of user@domain:

       1) user@domain
              This table lookup is always done and has the highest precedence.

       2) user
              This  table  lookup  is  done  only  when the domain part of the
              sender address matches $myorigin,  $mydestination,  $inet_inter-
              faces or $proxy_interfaces.

       3) @domain
              This table lookup is done last and has the lowest precedence.

       In all cases the result of table lookup must be either "not found" or a
       list of SASL login names separated by comma and/or whitespace.

smtpd_sender_restrictions (default: empty)
       Optional restrictions that the Postfix SMTP server applies in the  con-
       text  of  a client MAIL FROM command.  See SMTPD_ACCESS_README, section
       "Delayed evaluation of SMTP access restriction lists" for a  discussion
       of evaluation context and time.

       The default is to permit everything.

       Specify  a list of restrictions, separated by commas and/or whitespace.
       Continue  long  lines  by  starting  the  next  line  with  whitespace.
       Restrictions  are applied in the order as specified; the first restric-
       tion that matches wins.

       The following restrictions are specific to the sender address  received
       with the MAIL FROM command.

       check_sender_access type:table
              Search  the  specified  access(5)  database  for  the  MAIL FROM
              address, domain, parent domains, or localpart@, and execute  the
              corresponding action.

       check_sender_a_access type:table
              Search the specified access(5) database for the IP addresses for
              the MAIL FROM domain,  and  execute  the  corresponding  action.
              Note:  a  result  of  "OK"  is  not  allowed for safety reasons.
              Instead, use DUNNO in  order  to  exclude  specific  hosts  from
              blacklists.  This feature is available in Postfix 3.0 and later.

       check_sender_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              MAIL FROM domain, and execute the corresponding action.  Note: a
              result of "OK" is not allowed for safety reasons.  Instead,  use
              DUNNO  in order to exclude specific hosts from blacklists.  This
              feature is available in Postfix 2.1 and later.

       check_sender_ns_access type:table
              Search the specified access(5) database for the DNS servers  for
              the  MAIL  FROM  domain,  and  execute the corresponding action.
              Note: a result of  "OK"  is  not  allowed  for  safety  reasons.
              Instead,  use  DUNNO  in  order  to  exclude specific hosts from
              blacklists.  This feature is available in Postfix 2.1 and later.

       reject_authenticated_sender_login_mismatch
              Enforces   the   reject_sender_login_mismatch   restriction  for
              authenticated clients only. This feature is available in Postfix
              version 2.1 and later.

       reject_known_sender_login_mismatch
              Apply  the reject_sender_login_mismatch restriction only to MAIL
              FROM addresses that are known in $smtpd_sender_login_maps.  This
              feature is available in Postfix version 2.11 and later.

       reject_non_fqdn_sender
              Reject  the  request  when  the  MAIL  FROM  address  is  not in
              fully-qualified domain form, as required by the RFC.
              The non_fqdn_reject_code parameter specifies the  response  code
              for rejected requests (default: 504).

       reject_rhsbl_sender rbl_domain=d.d.d.d
              Reject  the request when the MAIL FROM domain is listed with the
              A record "d.d.d.d" under rbl_domain  (Postfix  version  2.1  and
              later  only).   Each  "d"  is a number, or a pattern inside "[]"
              that contains one or more ";"-separated numbers or  number..num-
              ber  ranges (Postfix version 2.8 and later). If no "=d.d.d.d" is
              specified, reject the request  when  the  MAIL  FROM  domain  is
              listed with any A record under rbl_domain.
              The  maps_rbl_reject_code  parameter specifies the response code
              for rejected requests  (default:   554);  the  default_rbl_reply
              parameter   specifies   the   default   server  reply;  and  the
              rbl_reply_maps parameter specifies tables  with  server  replies
              indexed by rbl_domain.  This feature is available in Postfix 2.0
              and later.

       reject_sender_login_mismatch
              Reject the request when  $smtpd_sender_login_maps  specifies  an
              owner  for  the  MAIL FROM address, but the client is not (SASL)
              logged in as that MAIL FROM address owner; or when the client is
              (SASL) logged in, but the client login name doesn't own the MAIL
              FROM address according to $smtpd_sender_login_maps.

       reject_unauthenticated_sender_login_mismatch
              Enforces the reject_sender_login_mismatch restriction for  unau-
              thenticated  clients  only. This feature is available in Postfix
              version 2.1 and later.

       reject_unknown_sender_domain
              Reject the request when Postfix is not final destination for the
              sender address, and the MAIL FROM domain has 1) no DNS MX and no
              DNS A record, or 2) a malformed MX record such as a record  with
              a zero-length MX hostname (Postfix version 2.3 and later).
              The  reply  is  specified  with  the unknown_address_reject_code
              parameter   (default:   450),    unknown_address_tempfail_action
              (default:  defer_if_permit),  or  550  (nullmx,  Postfix 3.0 and
              later). See the respective parameter descriptions for details.

       reject_unlisted_sender
              Reject the request when the MAIL FROM address is not  listed  in
              the  list  of  valid  recipients  for  its domain class. See the
              smtpd_reject_unlisted_sender parameter description for  details.
              This feature is available in Postfix 2.1 and later.

       reject_unverified_sender
              Reject  the  request when mail to the MAIL FROM address is known
              to bounce, or when the sender address destination is not  reach-
              able.   Address  verification information is managed by the ver-
              ify(8) server;  see  the  ADDRESS_VERIFICATION_README  file  for
              details.
              The unverified_sender_reject_code parameter specifies the numer-
              ical response code when an address is known to bounce  (default:
              450,  change  into 550 when you are confident that it is safe to
              do so).
              The   unverified_sender_defer_code   specifies   the   numerical
              response  code  when  an address probe failed due to a temporary
              problem (default: 450).
              The unverified_sender_tempfail_action  parameter  specifies  the
              action  after  address  probe failure due to a temporary problem
              (default: defer_if_permit).
              This feature is available in Postfix 2.1 and later.

       Other restrictions that are valid in this context:

             Generic restrictions that can be used in any SMTP  command  con-
              text, described under smtpd_client_restrictions.

             SMTP    command    specific    restrictions    described   under
              smtpd_client_restrictions and smtpd_helo_restrictions.

             SMTP command specific restrictions described under smtpd_recipi-
              ent_restrictions.  When  recipient restrictions are listed under
              smtpd_sender_restrictions,   they   have   effect   only    with
              "smtpd_delay_reject  =  yes", so that $smtpd_sender_restrictions
              is evaluated at the time of the RCPT TO command.

       Examples:

       smtpd_sender_restrictions = reject_unknown_sender_domain
       smtpd_sender_restrictions = reject_unknown_sender_domain,
           check_sender_access hash:/etc/postfix/access

smtpd_service_name (default: smtpd)
       The internal service that postscreen(8) hands off  allowed  connections
       to. In a future version there may be different classes of SMTP service.

       This feature is available in Postfix 2.8.

smtpd_soft_error_limit (default: 10)
       The number of errors a remote SMTP client is allowed  to  make  without
       delivering  mail  before  the  Postfix  SMTP  server slows down all its
       responses.

             With Postfix version 2.1 and  later,  the  Postfix  SMTP  server
              delays all responses by $smtpd_error_sleep_time seconds.

             With  Postfix  versions 2.0 and earlier, the Postfix SMTP server
              delays all responses by (number of errors) seconds.

smtpd_starttls_timeout (default: see postconf -d output)
       The time limit for Postfix SMTP server write and read operations during
       TLS  startup  and  shutdown  handshake  procedures. The current default
       value is stress-dependent. Before Postfix version 2.8, it was fixed  at
       300s.

       This feature is available in Postfix 2.2 and later.

smtpd_timeout (default: normal: 300s, overload: 10s)
       The  time  limit  for  sending  a  Postfix SMTP server response and for
       receiving a remote SMTP client request. Normally the default  limit  is
       300s,  but  it changes under overload to just 10s. With Postfix 2.5 and
       earlier, the SMTP server always uses a time limit of 300s by default.

       Note: if you set SMTP time limits to very large values you may have  to
       update the global ipc_timeout parameter.

       Time  units:  s (seconds), m (minutes), h (hours), d (days), w (weeks).
       The default time unit is s (seconds).

smtpd_tls_CAfile (default: empty)
       A file containing (PEM format) CA certificates of root CAs  trusted  to
       sign either remote SMTP client certificates or intermediate CA certifi-
       cates.  These are loaded into memory before the smtpd(8) server  enters
       the  chroot  jail.  If  the  number of trusted roots is large, consider
       using smtpd_tls_CApath instead, but note that the latter directory must
       be  present in the chroot jail if the smtpd(8) server is chrooted. This
       file may also be used to augment the server  certificate  trust  chain,
       but it is best to include all the required certificates directly in the
       server certificate file.

       Specify "smtpd_tls_CAfile = /path/to/system_CA_file" to  use  ONLY  the
       system-supplied default Certification Authority certificates.

       Specify  "tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party  certificates.

       By  default  (see  smtpd_tls_ask_ccert),  client  certificates  are not
       requested, and smtpd_tls_CAfile should remain empty. If you do make use
       of client certificates, the distinguished names (DNs) of the Certifica-
       tion Authorities listed in smtpd_tls_CAfile are sent to the remote SMTP
       client  in  the  client certificate request message. MUAs with multiple
       client certificates may use the list of preferred Certification Author-
       ities  to  select  the correct client certificate.  You may want to put
       your "preferred" CA or CAs in this file, and install other trusted  CAs
       in $smtpd_tls_CApath.

       Example:

       smtpd_tls_CAfile = /etc/postfix/CAcert.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_CApath (default: empty)
       A directory containing (PEM format) CA certificates of root CAs trusted
       to sign either remote SMTP client certificates or intermediate CA  cer-
       tificates. Do not forget to create the necessary "hash" links with, for
       example,  "$OPENSSL_HOME/bin/c_rehash   /etc/postfix/certs".   To   use
       smtpd_tls_CApath  in  chroot  mode,  this directory (or a copy) must be
       inside the chroot jail.

       Specify "smtpd_tls_CApath = /path/to/system_CA_directory" to  use  ONLY
       the system-supplied default Certification Authority certificates.

       Specify  "tls_append_default_CA = no" to prevent Postfix from appending
       the system-supplied default CAs and trusting third-party  certificates.

       By  default  (see  smtpd_tls_ask_ccert),  client  certificates  are not
       requested, and smtpd_tls_CApath should remain  empty.  In  contrast  to
       smtpd_tls_CAfile,   DNs   of  Certification  Authorities  installed  in
       $smtpd_tls_CApath are not included in the  client  certificate  request
       message.  MUAs  with  multiple  client certificates may use the list of
       preferred Certification Authorities to select the correct  client  cer-
       tificate.   You  may  want  to  put  your  "preferred"  CA  or  CAs  in
       $smtpd_tls_CAfile,  and  install   the   remaining   trusted   CAs   in
       $smtpd_tls_CApath.

       Example:

       smtpd_tls_CApath = /etc/postfix/certs

       This feature is available in Postfix 2.2 and later.

smtpd_tls_always_issue_session_ids (default: yes)
       Force  the Postfix SMTP server to issue a TLS session id, even when TLS
       session caching  is  turned  off  (smtpd_tls_session_cache_database  is
       empty). This behavior is compatible with Postfix < 2.3.

       With  Postfix 2.3 and later the Postfix SMTP server can disable session
       id generation when TLS session caching is turned off. This keeps remote
       SMTP  clients  from  caching  sessions  that almost certainly cannot be
       re-used.

       By default, the Postfix SMTP server always generates TLS  session  ids.
       This works around a known defect in mail client applications such as MS
       Outlook, and may also prevent interoperability issues with other  MTAs.

       Example:

       smtpd_tls_always_issue_session_ids = no

       This feature is available in Postfix 2.3 and later.

smtpd_tls_ask_ccert (default: no)
       Ask  a remote SMTP client for a client certificate. This information is
       needed for certificate based mail relaying with, for example, the  per-
       mit_tls_clientcerts feature.

       Some clients such as Netscape will either complain if no certificate is
       available (for the list of CAs in $smtpd_tls_CAfile) or will offer mul-
       tiple client certificates to choose from. This may be annoying, so this
       option is "off" by default.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_auth_only (default: no)
       When TLS encryption is optional in the  Postfix  SMTP  server,  do  not
       announce or accept SASL authentication over unencrypted connections.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_ccert_verifydepth (default: 9)
       The  verification depth for remote SMTP client certificates. A depth of
       1 is sufficient if the issuing CA is listed in a local CA file.

       The default verification depth is 9 (the OpenSSL default) for  compati-
       bility with earlier Postfix behavior. Prior to Postfix 2.5, the default
       value was 5, but the limit was not actually enforced. If you  have  set
       this  to  a  lower  non-default  value,  certificates with longer trust
       chains may now fail to verify. Certificate chains with 1 or 2  CAs  are
       common,  deeper  chains  are  more  rare and any number between 5 and 9
       should suffice in practice. You can choose a lower number if, for exam-
       ple,  you  trust  certificates directly signed by an issuing CA but not
       any CAs it delegates to.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cert_file (default: empty)
       File with the Postfix SMTP server RSA certificate in PEM format.   This
       file may also contain the Postfix SMTP server private RSA key.

       Public  Internet  MX hosts without certificates signed by a "reputable"
       CA must generate, and  be  prepared  to  present  to  most  clients,  a
       self-signed  or  private-CA  signed certificate. The client will not be
       able to authenticate the server, but unless it is running  Postfix  2.3
       or similar software, it will still insist on a server certificate.

       For servers that are not public Internet MX hosts, Postfix 2.3 supports
       configurations with no certificates. This entails the use of  just  the
       anonymous TLS ciphers, which are not supported by typical SMTP clients.
       Since such clients will not, as a rule, fall back to plain text after a
       TLS  handshake failure, the server will be unable to receive email from
       TLS enabled clients. To avoid accidental configurations  with  no  cer-
       tificates, Postfix 2.3 enables certificate-less operation only when the
       administrator  explicitly  sets  "smtpd_tls_cert_file  =  none".   This
       ensures  that new Postfix configurations will not accidentally run with
       no certificates.

       Both RSA and DSA certificates  are  supported.   When  both  types  are
       present, the cipher used determines which certificate will be presented
       to the client.  For Netscape and OpenSSL clients without special cipher
       choices the RSA certificate is preferred.

       To  enable  a remote SMTP client to verify the Postfix SMTP server cer-
       tificate, the issuing CA certificates must be  made  available  to  the
       client. You should include the required certificates in the server cer-
       tificate file, the server certificate first,  then  the  issuing  CA(s)
       (bottom-up order).

       Example: the certificate for "server.example.com" was issued by "inter-
       mediate CA" which itself has a certificate of "root  CA".   Create  the
       server.pem   file   with   "cat   server_cert.pem   intermediate_CA.pem
       root_CA.pem > server.pem".

       If you also want to verify client certificates issued by these CAs, you
       can  add  the CA certificates to the smtpd_tls_CAfile, in which case it
       is  not  necessary  to  have  them  in   the   smtpd_tls_cert_file   or
       smtpd_tls_dcert_file.

       A certificate supplied here must be usable as an SSL server certificate
       and hence pass the "openssl verify -purpose sslserver ..." test.

       Example:

       smtpd_tls_cert_file = /etc/postfix/server.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_cipherlist (default: empty)
       Obsolete Postfix < 2.3 control for the Postfix SMTP server  TLS  cipher
       list.  It  is  easy  to  create interoperability problems by choosing a
       non-default cipher list. Do not use a non-default TLS cipherlist for MX
       hosts on the public Internet. Clients that begin the TLS handshake, but
       are unable to agree on a common cipher, may not be  able  to  send  any
       email  to  the  SMTP server. Using a restricted cipher list may be more
       appropriate for a dedicated MSA or an internal mailhub, where  one  can
       exert some control over the TLS software and settings of the connecting
       clients.

       Note: do not use "" quotes around the parameter value.

       This feature is available with Postfix version 2.2. It is not used with
       Postfix 2.3 and later; use smtpd_tls_mandatory_ciphers instead.

smtpd_tls_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP server will use with
       opportunistic    TLS    encryption.    Cipher    types    listed     in
       smtpd_tls_exclude_ciphers  are excluded from the base definition of the
       selected cipher grade.  The  default  value  is  "medium"  for  Postfix
       releases after the middle of 2015, "export" for older releases.

       When   TLS   is   mandatory   the   cipher  grade  is  chosen  via  the
       smtpd_tls_mandatory_ciphers configuration parameter, see there for syn-
       tax details.

       This  feature is available in Postfix 2.6 and later. With earlier Post-
       fix releases only the smtpd_tls_mandatory_ciphers parameter  is  imple-
       mented, and opportunistic TLS always uses "export" or better (i.e. all)
       ciphers.

smtpd_tls_dcert_file (default: empty)
       File with the Postfix SMTP server DSA certificate in PEM format.   This
       file may also contain the Postfix SMTP server private DSA key.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_dcert_file = /etc/postfix/server-dsa.pem

       This feature is available in Postfix 2.2 and later.

smtpd_tls_dh1024_param_file (default: empty)
       File  with  DH  parameters that the Postfix SMTP server should use with
       non-export EDH ciphers.

       Instead of using the exact same  parameter  sets  as  distributed  with
       other  TLS  packages,  it  is  more  secure to generate your own set of
       parameters with something like the following commands:

           openssl dhparam -out /etc/postfix/dh512.pem 512
           openssl dhparam -out /etc/postfix/dh1024.pem 1024
           openssl dhparam -out /etc/postfix/dh2048.pem 2048

       It is safe to share the same DH  parameters  between  multiple  Postfix
       instances.   If  you  prefer,  you can generate separate parameters for
       each instance.

       If you want to take maximal advantage of  ciphers  that  offer  forward
       secrecy see the Getting started section of FORWARD_SECRECY_README.  The
       full document conveniently presents all information about Postfix "per-
       fect"  forward  secrecy  support in one place: what forward secrecy is,
       how to tweak settings, and what you can expect to see when Postfix uses
       ciphers with forward secrecy.

       Example:

       smtpd_tls_dh1024_param_file = /etc/postfix/dh2048.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dh512_param_file (default: empty)
       File  with  DH  parameters that the Postfix SMTP server should use with
       export-grade EDH ciphers.  The default  SMTP  server  cipher  grade  is
       "medium"  with  Postfix  releases  after  the  middle of 2015, and as a
       result export-grade cipher suites are by default not used.

       See also the discussion under the smtpd_tls_dh1024_param_file  configu-
       ration parameter.

       Example:

       smtpd_tls_dh512_param_file = /etc/postfix/dh_512.pem

       This feature is available with Postfix version 2.2.

smtpd_tls_dkey_file (default: $smtpd_tls_dcert_file)
       File  with the Postfix SMTP server DSA private key in PEM format.  This
       file may be combined with the Postfix SMTP server DSA certificate  file
       specified with $smtpd_tls_dcert_file.

       The  private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_eccert_file (default: empty)
       File  with  the  Postfix  SMTP  server ECDSA certificate in PEM format.
       This file may also contain the Postfix SMTP server private ECDSA key.

       See the discussion under smtpd_tls_cert_file for more details.

       Example:

       smtpd_tls_eccert_file = /etc/postfix/ecdsa-scert.pem

       This feature is available in Postfix 2.6 and  later,  when  Postfix  is
       compiled and linked with OpenSSL 1.0.0 or later.

smtpd_tls_eckey_file (default: $smtpd_tls_eccert_file)
       File  with  the  Postfix  SMTP  server ECDSA private key in PEM format.
       This file may be combined with the Postfix SMTP server  ECDSA  certifi-
       cate file specified with $smtpd_tls_eccert_file.

       The  private key must be accessible without a pass-phrase, i.e. it must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

       This  feature  is  available  in Postfix 2.6 and later, when Postfix is
       compiled and linked with OpenSSL 1.0.0 or later.

smtpd_tls_eecdh_grade (default: see postconf -d output)
       The Postfix SMTP server security  grade  for  ephemeral  elliptic-curve
       Diffie-Hellman (EECDH) key exchange.

       The available choices are:

       none   Don't  use  EECDH.  Ciphers  based on EECDH key exchange will be
              disabled. This is the default in Postfix versions 2.6 and 2.7.

       strong Use EECDH with approximately 128 bits of security at  a  reason-
              able  computational  cost.  This  is  the  current best-practice
              trade-off between security and computational efficiency. This is
              the default in Postfix version 2.8 and later.

       ultra  Use  EECDH  with  approximately 192 bits of security at computa-
              tional cost that is approximately  twice  as  high  as  128  bit
              strength  ECC. Barring significant progress in attacks on ellip-
              tic curve crypto-systems, the "strong" curve is  sufficient  for
              most users.

       If  you  want  to  take maximal advantage of ciphers that offer forward
       secrecy see the Getting started section of FORWARD_SECRECY_README.  The
       full document conveniently presents all information about Postfix "per-
       fect" forward secrecy support in one place: what  forward  secrecy  is,
       how to tweak settings, and what you can expect to see when Postfix uses
       ciphers with forward secrecy.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 1.0.0 or later on platforms where EC algorithms
       have not been disabled by the vendor.

smtpd_tls_exclude_ciphers (default: empty)
       List of ciphers or cipher types to exclude from the SMTP server  cipher
       list  at  all  TLS  security levels. Excluding valid ciphers can create
       interoperability problems. DO NOT exclude ciphers unless it  is  essen-
       tial  to  do so. This is not an OpenSSL cipherlist; it is a simple list
       separated by whitespace  and/or  commas.  The  elements  are  a  single
       cipher,  or  one or more "+" separated cipher properties, in which case
       only ciphers matching all the properties are excluded.

       Examples (some of these will cause problems):

           smtpd_tls_exclude_ciphers = aNULL
           smtpd_tls_exclude_ciphers = MD5, DES
           smtpd_tls_exclude_ciphers = DES+MD5
           smtpd_tls_exclude_ciphers = AES256-SHA, DES-CBC3-MD5
           smtpd_tls_exclude_ciphers = kEDH+aRSA

       The first setting disables anonymous ciphers. The next setting disables
       ciphers  that  use the MD5 digest algorithm or the (single) DES encryp-
       tion algorithm. The next setting disables ciphers that use MD5 and  DES
       together.   The  next setting disables the two ciphers "AES256-SHA" and
       "DES-CBC3-MD5". The last setting disables ciphers that  use  "EDH"  key
       exchange with RSA authentication.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_fingerprint_digest (default: md5)
       The  message  digest algorithm to construct remote SMTP client-certifi-
       cate fingerprints or public key fingerprints (Postfix  2.9  and  later)
       for  check_ccert_access  and  permit_tls_clientcerts. The default algo-
       rithm is md5, for backwards compatibility with Postfix  releases  prior
       to 2.5.

       Advances  in  hash  function cryptanalysis have led to md5 being depre-
       cated in favor of sha1.  However, as long as there are no known "second
       pre-image"  attacks  against  md5, its use in this context can still be
       considered safe.

       While additional digest algorithms are often available  with  OpenSSL's
       libcrypto, only those used by libssl in SSL cipher suites are available
       to Postfix.

       To find the fingerprint of a specific certificate file, with a specific
       digest algorithm, run:

           $ openssl x509 -noout -fingerprint -digest -in certfile.pem

       The  text  to  the  right  of "=" sign is the desired fingerprint.  For
       example:

           $ openssl x509 -noout -fingerprint -sha1 -in cert.pem
           SHA1 Fingerprint=D4:6A:AB:19:24:79:F8:32:BB:A6:CB:66:82:C0:8E:9B:EE:29:A8:1A

       To extract the public key fingerprint from an  X.509  certificate,  you
       need  to  extract  the  public key from the certificate and compute the
       appropriate digest of its DER (ASN.1) encoding. With OpenSSL the "-pub-
       key"  option  of  the  "x509" command extracts the public key always in
       "PEM" format. We pipe the result to another OpenSSL command  that  con-
       verts the key to DER and then to the "dgst" command to compute the fin-
       gerprint.

       The actual command to transform the key to DER format  depends  on  the
       version  of OpenSSL used. With OpenSSL 1.0.0 and later, the "pkey" com-
       mand supports all key types. With OpenSSL 0.9.8 and  earlier,  the  key
       type  is  always  RSA  (nobody uses DSA, and EC keys are not fully sup-
       ported by 0.9.8), so the "rsa" command is used.

           # OpenSSL 1.0 with all certificates and SHA-1 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl pkey -pubin -outform DER |
               openssl dgst -sha1 -c
           (stdin)= 64:3f:1f:f6:e5:1e:d4:2a:56:8b:fc:09:1a:61:98:b5:bc:7c:60:58

           # OpenSSL 0.9.8 with RSA certificates and MD5 fingerprints.
           $ openssl x509 -in cert.pem -noout -pubkey |
               openssl rsa -pubin -outform DER |
               openssl dgst -md5 -c
           (stdin)= f4:62:60:f6:12:8f:d5:8d:28:4d:13:a7:db:b2:ff:50

       The Postfix SMTP server and client log the peer (leaf) certificate fin-
       gerprint  and  public  key  fingerprint  when  the TLS loglevel is 2 or
       higher.

       Note: Postfix 2.9.0-2.9.5 computed the public  key  fingerprint  incor-
       rectly.  To  use  public-key  fingerprints, upgrade to Postfix 2.9.6 or
       later.

       Example: client-certificate access table, with sha1 fingerprints:

           /etc/postfix/main.cf:
               smtpd_tls_fingerprint_digest = sha1
               smtpd_client_restrictions =
                   check_ccert_access hash:/etc/postfix/access,
                   reject
           /etc/postfix/access:
               # Action folded to next line...
               AF:88:7C:AD:51:95:6F:36:96:F6:01:FB:2E:48:CD:AB:49:25:A2:3B
                   OK
               85:16:78:FD:73:6E:CE:70:E0:31:5F:0D:3C:C8:6D:C4:2C:24:59:E1
                   permit_auth_destination

       This feature is available in Postfix 2.5 and later.

smtpd_tls_key_file (default: $smtpd_tls_cert_file)
       File with the Postfix SMTP server RSA private key in PEM format.   This
       file  may be combined with the Postfix SMTP server RSA certificate file
       specified with $smtpd_tls_cert_file.

       The private key must be accessible without a pass-phrase, i.e. it  must
       not be encrypted. File permissions should grant read-only access to the
       system superuser account ("root"), and no access to anyone else.

smtpd_tls_loglevel (default: 0)
       Enable additional Postfix SMTP server logging of  TLS  activity.   Each
       logging  level  also includes the information that is logged at a lower
       logging level.

              0 Disable logging of TLS activity.

              1 Log only a summary message on TLS handshake  completion  -  no
              logging of client certificate trust-chain verification errors if
              client certificate verification is not required.   With  Postfix
              2.8  and earlier, log the summary message, peer certificate sum-
              mary information and unconditionally log  trust-chain  verifica-
              tion errors.

              2 Also log levels during TLS negotiation.

              3  Also  log  hexadecimal  and  ASCII  dump  of  TLS negotiation
              process.

              4 Also log hexadecimal and ASCII dump of  complete  transmission
              after STARTTLS.

       Do  not  use "smtpd_tls_loglevel = 2" or higher except in case of prob-
       lems. Use of loglevel 4 is strongly discouraged.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_mandatory_ciphers (default: medium)
       The minimum TLS cipher grade that the Postfix SMTP server will use with
       mandatory  TLS encryption. The default grade ("medium") is sufficiently
       strong that any benefit from globally restricting  TLS  sessions  to  a
       more  stringent  grade  is likely negligible, especially given the fact
       that many implementations still  do  not  offer  any  stronger  ("high"
       grade)  ciphers,  while  those  that  do,  will always use "high" grade
       ciphers. So insisting on "high" grade ciphers is generally counter-pro-
       ductive.  Allowing  "export"  or  "low" ciphers is typically not a good
       idea, as  systems  limited  to  just  these  are  limited  to  obsolete
       browsers.  No  known SMTP clients fail to support at least one "medium"
       or "high" grade cipher.

       The following cipher grades are supported:

       export Enable "EXPORT" grade or stronger OpenSSL ciphers.  The underly-
              ing  cipherlist  is specified via the tls_export_cipherlist con-
              figuration parameter, which you are strongly encouraged  to  not
              change.  This choice is insecure and SHOULD NOT be used.

       low    Enable  "LOW"  grade or stronger OpenSSL ciphers. The underlying
              cipherlist is specified via the tls_low_cipherlist configuration
              parameter,  which  you  are  strongly  encouraged to not change.
              This choice is insecure and SHOULD NOT be used.

       medium Enable "MEDIUM" grade or stronger  OpenSSL  ciphers.  These  use
              128-bit  or  longer  symmetric bulk-encryption keys. This is the
              default minimum  strength  for  mandatory  TLS  encryption.  The
              underlying cipherlist is specified via the tls_medium_cipherlist
              configuration parameter, which you are  strongly  encouraged  to
              not change.

       high   Enable   only  "HIGH"  grade  OpenSSL  ciphers.  The  underlying
              cipherlist is specified via the  tls_high_cipherlist  configura-
              tion parameter, which you are strongly encouraged to not change.

       null   Enable only the "NULL" OpenSSL ciphers, these provide  authenti-
              cation  without encryption.  This setting is only appropriate in
              the rare case that all clients are prepared to use NULL  ciphers
              (not normally enabled in TLS clients). The underlying cipherlist
              is specified via the tls_null_cipherlist  configuration  parame-
              ter, which you are strongly encouraged to not change.

       Cipher   types   listed   in   smtpd_tls_mandatory_exclude_ciphers   or
       smtpd_tls_exclude_ciphers are excluded from the base definition of  the
       selected  cipher  grade. See smtpd_tls_ciphers for cipher controls that
       apply to opportunistic TLS.

       The underlying cipherlists for grades other than "null" include  anony-
       mous ciphers, but these are automatically filtered out if the server is
       configured to ask for remote SMTP client certificates.   You  are  very
       unlikely  to  need to take any steps to exclude anonymous ciphers, they
       are excluded automatically as required.  If you must exclude  anonymous
       ciphers  even  when Postfix does not need or use peer certificates, set
       "smtpd_tls_exclude_ciphers = aNULL". To exclude anonymous ciphers  only
       when   TLS  is  enforced,  set  "smtpd_tls_mandatory_exclude_ciphers  =
       aNULL".

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_exclude_ciphers (default: empty)
       Additional list of ciphers or cipher types to exclude from the  Postfix
       SMTP  server  cipher  list at mandatory TLS security levels.  This list
       works    in    addition    to    the     exclusions     listed     with
       smtpd_tls_exclude_ciphers (see there for syntax details).

       This feature is available in Postfix 2.3 and later.

smtpd_tls_mandatory_protocols (default: !SSLv2, !SSLv3)
       The  SSL/TLS  protocols accepted by the Postfix SMTP server with manda-
       tory TLS encryption. If the list is  empty,  the  server  supports  all
       available  SSL/TLS  protocol  versions.  A non-empty value is a list of
       protocol names separated by whitespace, commas  or  colons.   The  sup-
       ported  protocol  names  are  "SSLv2", "SSLv3" and "TLSv1", and are not
       case sensitive. The default  value  is  "!SSLv2,  !SSLv3"  for  Postfix
       releases after the middle of 2015, "!SSLv2" for older releases.

       With Postfix >= 2.5 the parameter syntax was expanded to support proto-
       col  exclusions.  One  can  explicitly  exclude  "SSLv2"   by   setting
       "smtpd_tls_mandatory_protocols  =  !SSLv2". To exclude both "SSLv2" and
       "SSLv3" set "smtpd_tls_mandatory_protocols = !SSLv2,  !SSLv3".  Listing
       the  protocols  to  include,  rather than protocols to exclude, is sup-
       ported, but not recommended. The exclusion form  more  closely  matches
       the underlying OpenSSL interface semantics.

       Note:  As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and
       "TLSv1.2". When Postfix <= 2.5  is  linked  against  OpenSSL  1.0.1  or
       later,  these,  or any other new protocol versions, cannot be disabled.
       The latest patch levels of Postfix >= 2.6, and all versions of  Postfix
       >= 2.10 can disable support for "TLSv1.1" or "TLSv1.2".

       Example:

       # Preferred syntax with Postfix >= 2.5:
       smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3
       # Legacy syntax:
       smtpd_tls_mandatory_protocols = TLSv1

       This feature is available in Postfix 2.3 and later.

smtpd_tls_protocols (default: !SSLv2, !SSLv3)
       List  of  TLS  protocols  that  the Postfix SMTP server will exclude or
       include  with  opportunistic  TLS  encryption.  The  default  value  is
       "!SSLv2,  !SSLv3"  for Postfix releases after the middle of 2015, empty
       for older releases allowing all protocols to be used with opportunistic
       TLS.  A non-empty value is a list of protocol names separated by white-
       space, commas or colons.  The supported  protocol  names  are  "SSLv2",
       "SSLv3" and "TLSv1", and are not case sensitive.

       Note:  As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and
       "TLSv1.2". The latest patch levels of Postfix >= 2.6, and all  versions
       of Postfix >= 2.10 can disable support for "TLSv1.1" or "TLSv1.2".

       To  include  a  protocol  list its name, to exclude it, prefix the name
       with a "!" character.  To  exclude  SSLv2  for  opportunistic  TLS  set
       "smtpd_tls_protocols = !SSLv2". To exclude both "SSLv2" and "SSLv3" set
       "smtpd_tls_protocols = !SSLv2, !SSLv3". Explicitly listing  the  proto-
       cols  to  include,  rather than protocols to exclude, is supported, but
       not recommended.  The exclusion form more closely matches the  underly-
       ing OpenSSL interface semantics.

       Example:
       smtpd_tls_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.6 and later.

smtpd_tls_received_header (default: no)
       Request  that the Postfix SMTP server produces Received:  message head-
       ers that include information about the protocol  and  cipher  used,  as
       well as the remote SMTP client CommonName and client certificate issuer
       CommonName.  This is disabled by default, as  the  information  may  be
       modified  in transit through other mail servers.  Only information that
       was recorded by the final destination can be trusted.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_req_ccert (default: no)
       With mandatory TLS encryption, require a  trusted  remote  SMTP  client
       certificate  in order to allow TLS connections to proceed.  This option
       implies "smtpd_tls_ask_ccert = yes".

       When TLS encryption is optional, this setting is ignored with a warning
       written to the mail log.

       This feature is available in Postfix 2.2 and later.

smtpd_tls_security_level (default: empty)
       The  SMTP  TLS  security  level  for  the  Postfix  SMTP server; when a
       non-empty value is specified, this overrides  the  obsolete  parameters
       smtpd_use_tls  and  smtpd_enforce_tls.  This  parameter is ignored with
       "smtpd_tls_wrappermode = yes".

       Specify one of the following security levels:

       none   TLS will not be used.

       may    Opportunistic TLS: announce  STARTTLS  support  to  remote  SMTP
              clients, but do not require that clients use TLS encryption.

       encrypt
              Mandatory  TLS  encryption:  announce STARTTLS support to remote
              SMTP clients, and  require  that  clients  use  TLS  encryption.
              According to RFC 2487 this MUST NOT be applied in case of a pub-
              licly-referenced SMTP server. Instead,  this  option  should  be
              used only on dedicated servers.

       Note  1:  the  "fingerprint", "verify" and "secure" levels are not sup-
       ported here.  The Postfix SMTP server logs a warning and uses "encrypt"
       instead.  To verify remote SMTP client certificates, see TLS_README for
       a discussion of the smtpd_tls_ask_ccert, smtpd_tls_req_ccert, and  per-
       mit_tls_clientcerts features.

       Note  2:  The  parameter  setting  "smtpd_tls_security_level = encrypt"
       implies "smtpd_tls_auth_only = yes".

       Note 3: when invoked via  "sendmail  -bs",  Postfix  will  never  offer
       STARTTLS  due  to  insufficient privileges to access the server private
       key. This is intended behavior.

       This feature is available in Postfix 2.3 and later.

smtpd_tls_session_cache_database (default: empty)
       Name of the file containing the optional Postfix SMTP server  TLS  ses-
       sion  cache. Specify a database type that supports enumeration, such as
       btree or sdbm; there is no need to support concurrent access.  The file
       is  created if it does not exist. The smtpd(8) daemon does not use this
       parameter directly, rather the cache is implemented indirectly  in  the
       tlsmgr(8)  daemon.  This  means that per-smtpd-instance master.cf over-
       rides of this parameter are not effective. Note, that each of the cache
       databases supported by tlsmgr(8) daemon: $smtpd_tls_session_cache_data-
       base, $smtp_tls_session_cache_database (and with Postfix 2.3 and  later
       $lmtp_tls_session_cache_database), needs to be stored separately. It is
       not at this time possible to store multiple caches in  a  single  data-
       base.

       Note:  dbm  databases  are  not  suitable.  TLS session objects are too
       large.

       As of version 2.5, Postfix no longer uses root privileges when  opening
       this  file.  The  file  should  now  be  stored under the Postfix-owned
       data_directory. As a migration aid, an attempt to open the file under a
       non-Postfix  directory  is  redirected to the Postfix-owned data_direc-
       tory, and a warning is logged.

       As of Postfix 2.11 the preferred mechanism for  session  resumption  is
       RFC  5077 TLS session tickets, which don't require server-side storage.
       Consequently, for Postfix >= 2.11 this parameter  should  generally  be
       left  empty.   TLS session tickets require an OpenSSL library (at least
       version 0.9.8h) that provides full support for this TLS extension.  See
       also smtpd_tls_session_cache_timeout.

       Example:

       smtpd_tls_session_cache_database = btree:/var/db/postfix/smtpd_scache

       This feature is available in Postfix 2.2 and later.

smtpd_tls_session_cache_timeout (default: 3600s)
       The  expiration  time of Postfix SMTP server TLS session cache informa-
       tion. A cache cleanup is performed periodically  every  $smtpd_tls_ses-
       sion_cache_timeout  seconds. As with $smtpd_tls_session_cache_database,
       this parameter is implemented in the  tlsmgr(8)  daemon  and  therefore
       per-smtpd-instance master.cf overrides are not possible.

       As  of  Postfix 2.11 this setting cannot exceed 100 days.  If set <= 0,
       session caching is disabled, not just via the database,  but  also  via
       RFC  5077 TLS session tickets, which don't require server-side storage.
       If set to a positive value less than 2 minutes, the minimum value of  2
       minutes  is  used  instead.   TLS  session  tickets  require an OpenSSL
       library (at least version 0.9.8h) that provides full support  for  this
       TLS extension.

       This feature is available in Postfix 2.2 and later, and updated for TLS
       session ticket support in Postfix 2.11.

smtpd_tls_wrappermode (default: no)
       Run the Postfix SMTP server in the non-standard "wrapper" mode, instead
       of using the STARTTLS command.

       If  you  want  to  support  this service, enable a special port in mas-
       ter.cf, and specify "-o smtpd_tls_wrappermode=yes" on the SMTP server's
       command line. Port 465 (smtps) was once chosen for this purpose.

       This feature is available in Postfix 2.2 and later.

smtpd_upstream_proxy_protocol (default: empty)
       The  name  of the proxy protocol used by an optional before-smtpd proxy
       agent. When a proxy agent is used,  this  protocol  conveys  local  and
       remote       address      and      port      information.       Specify
       "smtpd_upstream_proxy_protocol = haproxy" to enable the haproxy  proto-
       col.

       NOTE: To use the nginx proxy with smtpd(8), enable the XCLIENT protocol
       with smtpd_authorized_xclient_hosts. This supports SASL  authentication
       in the proxy agent (Postfix 2.9 and later).

       This feature is available in Postfix 2.10 and later.

smtpd_upstream_proxy_timeout (default: 5s)
       The   time   limit   for   the   proxy   protocol  specified  with  the
       smtpd_upstream_proxy_protocol parameter.

       This feature is available in Postfix 2.10 and later.

smtpd_use_tls (default: no)
       Opportunistic TLS: announce STARTTLS support to  remote  SMTP  clients,
       but do not require that clients use TLS encryption.

       Note:  when invoked via "sendmail -bs", Postfix will never offer START-
       TLS due to insufficient privileges to access the  server  private  key.
       This is intended behavior.

       This  feature  is  available in Postfix 2.2 and later. With Postfix 2.3
       and later use smtpd_tls_security_level instead.

smtputf8_autodetect_classes (default: sendmail, verify)
       Detect that a message requires SMTPUTF8 support for the specified  mail
       origin classes.  This is a workaround to avoid chicken-and-egg problems
       during the initial SMTPUTF8 roll-out in environments with  pre-existing
       mail flows that contain UTF8. Those mail flows should not break because
       Postfix suddenly refuses to deliver such mail to down-stream MTAs  that
       don't announce SMTPUTF8 support.

       The problem is that Postfix cannot rely solely on the sender's declara-
       tion that a message requires SMTPUTF8  support,  because  UTF8  may  be
       introduced during local processing (for example, the client hostname in
       Postfix's Received: header,  adding  @$myorigin  or  .$mydomain  to  an
       incomplete  address,  address rewriting, alias expansion, automatic BCC
       recipients, local forwarding, and changes made by header checks or Mil-
       ter applications).

       For  now,  the  default  is to enable "SMTPUTF8 required" autodetection
       only for Postfix sendmail command-line submissions and address  verifi-
       cation  probes.   This  may change once SMTPUTF8 support achieves world
       domination.  However, sites that add UTF8 content via local  processing
       (see  above)  should  autodetect  the need for SMTPUTF8 support for all
       email.

       Specify one or more of the following:

        sendmail
              Submission with the Postfix sendmail(1) command.

        smtpd Mail received with the smtpd(8) daemon.

        qmqpd Mail received with the qmqpd(8) daemon.

        forward
              Local forwarding or aliasing.  When a message is  received  with
              "SMTPUTF8 required", then the forwarded (aliased) message always
              has "SMTPUTF8 required".

        bounce
              Submission by the bounce(8) daemon.  When a message is  received
              with  "SMTPUTF8 required", then the delivery status notification
              always has "SMTPUTF8 required".

        notify
              Postmaster notification from the smtp(8) or smtpd(8) daemon.

        verify
              Address verification probe from the verify(8) daemon.

        all   Enable SMTPUTF8 autodetection for all mail.

       This feature is available in Postfix 3.0 and later.

smtputf8_enable (default: yes)
       Enable preliminary SMTPUTF8 support for the protocols described in  RFC
       6531..6533. This requires that Postfix is built to support these proto-
       cols.

       This feature is available in Postfix 3.0 and later.

soft_bounce (default: no)
       Safety net to keep mail queued that would otherwise be returned to  the
       sender.  This parameter disables locally-generated bounces, changes the
       handling of negative responses from remote servers, content filters  or
       plugins,  and prevents the Postfix SMTP server from rejecting mail per-
       manently by changing 5xx reply codes into 4xx.  However, soft_bounce is
       no cure for address rewriting mistakes or mail routing mistakes.

       Note:  "soft_bounce  =  yes"  is in some cases implemented by modifying
       server responses. Therefore, the response that Postfix logs may  differ
       from the response that Postfix actually sends or receives.

       Example:

       soft_bounce = yes

stale_lock_time (default: 500s)
       The  time  after  which  a stale exclusive mailbox lockfile is removed.
       This is used for delivery to file or mailbox.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

stress (default: empty)
       This feature is documented in the STRESS_README document.

       This feature is available in Postfix 2.5 and later.

strict_7bit_headers (default: no)
       Reject  mail  with 8-bit text in message headers. This blocks mail from
       poorly written applications.

       This feature should not be enabled on a general  purpose  mail  server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime (default: no)
       Enable both strict_7bit_headers and strict_8bitmime_body.

       This  feature  should  not be enabled on a general purpose mail server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_8bitmime_body (default: no)
       Reject 8-bit message body text  without  8-bit  MIME  content  encoding
       information.  This blocks mail from poorly written applications.

       Unfortunately,  this  also rejects majordomo approval requests when the
       included request contains valid 8-bit MIME mail, and it rejects bounces
       from  mailers  that do not MIME encapsulate 8-bit content (for example,
       bounces from qmail or from old versions of Postfix).

       This feature should not be enabled on a general  purpose  mail  server,
       because it is likely to reject legitimate email.

       This feature is available in Postfix 2.0 and later.

strict_mailbox_ownership (default: yes)
       Defer  delivery when a mailbox file is not owned by its recipient.  The
       default setting is not backwards compatible.

       This feature is available in Postfix 2.5.3 and later.

strict_mime_encoding_domain (default: no)
       Reject mail with invalid Content-Transfer-Encoding: information for the
       message/*  or  multipart/*  MIME  content types.  This blocks mail from
       poorly written software.

       This feature should not be enabled on a general  purpose  mail  server,
       because it will reject mail after a single violation.

       This feature is available in Postfix 2.0 and later.

strict_rfc821_envelopes (default: no)
       Require  that addresses received in SMTP MAIL FROM and RCPT TO commands
       are enclosed with <>, and that those addresses do not contain  RFC  822
       style  comments  or phrases.  This stops mail from poorly written soft-
       ware.

       By default, the Postfix SMTP server accepts RFC 822 syntax in MAIL FROM
       and RCPT TO addresses.

strict_smtputf8 (default: no)
       Enable  stricter enforcement of the SMTPUTF8 protocol. The Postfix SMTP
       server accepts UTF8 sender or recipient addresses only when the  client
       requests an SMTPUTF8 mail transaction.

       This feature is available in Postfix 3.0 and later.

sun_mailtool_compatibility (default: no)
       Obsolete  SUN  mailtool  compatibility  feature.  Instead,  use  "mail-
       box_delivery_lock = dotlock".

swap_bangpath (default: yes)
       Enable the rewriting of "site!user" into "user@site".  This  is  neces-
       sary  if  your machine is connected to UUCP networks.  It is enabled by
       default.

       Note: with Postfix version 2.2, message header address  rewriting  hap-
       pens only when one of the following conditions is true:

             The message is received with the Postfix sendmail(1) command,

             The  message  is  received  from  a  network client that matches
              $local_header_rewrite_clients,

             The  message   is   received   from   the   network,   and   the
              remote_header_rewrite_domain  parameter  specifies  a  non-empty
              value.

       To   get   the   behavior   before   Postfix   version   2.2,   specify
       "local_header_rewrite_clients = static:all".

       Example:

       swap_bangpath = no

syslog_facility (default: mail)
       The  syslog  facility of Postfix logging. Specify a facility as defined
       in syslog.conf(5). The default facility is "mail".

       Warning: a non-default syslog_facility setting takes effect only  after
       a  Postfix process has completed initialization.  Errors during process
       initialization will be logged with the default facility.  Examples  are
       errors  while  parsing  the  command  line  arguments, and errors while
       accessing the Postfix main.cf configuration file.

syslog_name (default: see postconf -d output)
       The mail system name that is prepended to the process  name  in  syslog
       records, so that "smtpd" becomes, for example, "postfix/smtpd".

       Warning:  a  non-default  syslog_name setting takes effect only after a
       Postfix process has completed  initialization.  Errors  during  process
       initialization  will  be  logged  with  the  default name. Examples are
       errors while parsing the  command  line  arguments,  and  errors  while
       accessing the Postfix main.cf configuration file.

tcp_windowsize (default: 0)
       An  optional  workaround  for  routers  that  break TCP window scaling.
       Specify a value > 0 and < 65536 to enable this feature.   With  Postfix
       TCP  servers  (smtpd(8),  qmqpd(8)), this feature is implemented by the
       Postfix master(8) daemon.

       To change this parameter without stopping Postfix, you  need  to  first
       terminate all Postfix TCP servers:

           # postconf -e master_service_disable=inet
           # postfix reload

       This  immediately  terminates all processes that accept network connec-
       tions.  Next, you enable Postfix TCP servers with the updated  tcp_win-
       dowsize setting:

           # postconf -e tcp_windowsize=65535 master_service_disable=
           # postfix reload

       If  you  skip  these  steps  with  a  running  Postfix system, then the
       tcp_windowsize change will work only for Postfix TCP clients  (smtp(8),
       lmtp(8)).

       This feature is available in Postfix 2.6 and later.

tls_append_default_CA (default: no)
       Append the system-supplied default Certification Authority certificates
       to the ones specified with *_tls_CApath or *_tls_CAfile.   The  default
       is  "no";  this prevents Postfix from trusting third-party certificates
       and giving them relay permission with permit_tls_all_clientcerts.

       This feature is available in Postfix 2.4.15, 2.5.11, 2.6.8,  2.7.2  and
       later  versions.  Specify  "tls_append_default_CA  = yes" for backwards
       compatibility, to avoid breaking certificate  verification  with  sites
       that don't use permit_tls_all_clientcerts.

tls_daemon_random_bytes (default: 32)
       The  number  of pseudo-random bytes that an smtp(8) or smtpd(8) process
       requests from the tlsmgr(8) server in order to seed its internal pseudo
       random number generator (PRNG).  The default of 32 bytes (equivalent to
       256 bits) is sufficient to generate a 128bit (or 168bit) session key.

       This feature is available in Postfix 2.2 and later.

tls_dane_digest_agility (default: on)
       Configure DANE TLSA digest algorithm agility.   When  digest  algorithm
       agility  is  enabled, and the server and client support a common strong
       digest algorithm,  TLSA  records  with  weaker  digest  algorithms  are
       ignored.

       Specify one of the following:

       off    DANE  verification  examines each well-formed record in the TLSA
              RRset whose matching type is either "0" (no hash used) or is one
              of the digest algorithms listed in $tls_dane_digests.  This set-
              ting is not recommended.

       on     From each group of well-formed TLSA RRs a non-zero digest match-
              ing type with the same certificate usage and selector, DANE ver-
              ification examines only those records whose  matching  type  has
              the highest precedence (appear earliest in $tls_dane_digests).

       maybe  For  compatibility  with digest algorithm agility, each certifi-
              cate or public key whose digest  is  included  in  a  DANE  TLSA
              RRset,  SHOULD be published with the same set of digest matching
              type values as any other  with  the  same  usage  and  selector.
              Therefore,  compatible  TLSA  RRsets  will  contain an identical
              count of well-formed RRs with each non-zero digest matching type
              for any fixed combination of usage and selector.  When this con-
              straint is violated, or any of the digest records are malformed,
              digest algorithm agility will disabled.  Otherwise, digest algo-
              rithm agility is enabled.

       Digest algorithm agility ensures that the strongest digest supported by
       both  the Postfix SMTP client and the remote server is used, and weaker
       digests are ignored.  This supports non-disruptive deprecation of  out-
       dated digest algorithms.

       To  ensure compatibility with digest algorithm agility during key rota-
       tion, when a certificate or public key is being replaced with  another,
       and  both are published during the transition, both the old and the new
       certificate MUST be specified with the same set of  digests.   One  can
       change  the list of digest algorithms later, once old keys are retired.
       At any given time, change either the list of digests  without  changing
       the  list of certificates or public keys or the list of certificates or
       public keys without changing the list of digests.  Full value  matching
       type  "0"  records are not subject to this constraint, but are discour-
       aged due to the size of the resulting DNS records.

       It is expected that this algorithm agility mechanism will be  published
       in  a  standards  track RFC for SMTP with DANE, and also in an eventual
       update to RFC 6698.

       This feature is available in Postfix 2.11 and later.

tls_dane_digests (default: sha512 sha256)
       RFC 6698 TLSA resource-record  "matching  type"  digest  algorithms  in
       descending preference order.  All the specified algorithms must be sup-
       ported by the underlying OpenSSL library, otherwise  the  Postfix  SMTP
       client will not support DANE TLSA security.

       Specify  a  list of digest names separated by commas and/or whitespace.
       Each digest name may be followed by  an  optional  "=<number>"  suffix.
       For  example,  "sha512"  may  instead  be  specified  as "sha512=2" and
       "sha256" may instead be specified as "sha256=1".  The  optional  number
       must  match  the <a href="https://www.iana.org/assignments/dane-parame-
       ters/dane-parameters.xhtml#matching-types" >IANA assigned TLSA matching
       type  number  the  algorithm in question.  Postfix will check this con-
       straint for the algorithms it knows about.   Additional  matching  type
       algorithms registered with IANA can be added with explicit numbers pro-
       vided they are supported by OpenSSL.

       Invalid list elements are logged with a warning and disable  DANE  sup-
       port.   TLSA  RRs  that  specify  digests  not included in the list are
       ignored with a warning.

       Note: It is unwise to omit sha256 from the digest  list.   This  digest
       algorithm  is  the  only mandatory to implement digest algorithm in RFC
       6698, and many servers are expected  publish  TLSA  records  with  just
       sha256  digests.   Unless one of the standard digests is seriously com-
       promised and servers have had ample time to update their  TLSA  records
       you  should  not  omit any standard digests, just arrange them in order
       from strongest to weakest.

       When for a particular combination of "certificate usage" and "selector"
       the  TLSA  RRset  contains  records  with more than one digest matching
       type, the tls_dane_digest_agility parameter determines whether all  the
       RRs  are  used,  or  only those with the most preferred digest matching
       type.

       The tls_dane_trust_anchor_digest_enable parameter controls whether  any
       digest  TLSA  records  are acceptable in usage "2" (trust anchor asser-
       tion) TLSA records.

       This feature is available in Postfix 2.11 and later.

tls_dane_trust_anchor_digest_enable (default: yes)
       RFC 6698 trust-anchor  digest  support  in  the  Postfix  TLS  library.
       Enable  support  for  RFC  6698  (DANE  TLSA)  DNS records that contain
       digests of trust-anchors with certificate usage "2".  In this case  the
       certificate  usage  logically requires the server administrator to con-
       figure the server  to  include  the  trust-anchor  certificate  in  the
       server's  SSL  certificate  chain.  If enough domains mess this up, you
       can disable support for these TLSA records, but you'll no  longer  have
       secure  connections  that  get  it  right and only publish trust anchor
       records.

       At the dane security level, when a TLSA RRset  includes  only  unusable
       associations,  the  Postfix  SMTP  client will automatically switch the
       connection to the encrypt security level.  At  the  dane-only  security
       level, the server in question is skipped and delivery is deferred if no
       secure servers are found.

       The tls_dane_digests parameter controls the list of  digest  algorithms
       that are supported in TLSA records.  The tls_dane_digest_agility param-
       eter controls digest algorithm downgrade attack resistance.

       This feature is available in Postfix 2.11 and later.

tls_disable_workarounds (default: see postconf -d output)
       List or bit-mask of OpenSSL bug work-arounds to disable.

       The OpenSSL toolkit includes a set of work-arounds  for  buggy  SSL/TLS
       implementations.  Applications,  such as Postfix, that want to maximize
       interoperability ask the OpenSSL library to enable the full set of rec-
       ommended work-arounds.

       From  time to time, it is discovered that a work-around creates a secu-
       rity issue, and should no longer be used. If  upgrading  OpenSSL  to  a
       fixed  version  is  not  an  option or an upgrade is not available in a
       timely manner, or in closed environments  where  no  buggy  clients  or
       servers  exist,  it  may  be  appropriate to disable some or all of the
       OpenSSL interoperability work-arounds. This parameter  specifies  which
       bug work-arounds to disable.

       If  the  value  of the parameter is a hexadecimal long integer starting
       with "0x", the bug work-arounds corresponding to the bits specified  in
       its  value  are  removed  from the SSL_OP_ALL work-around bit-mask (see
       openssl/ssl.h and SSL_CTX_set_options(3)). You can  specify  more  bits
       than  are  present  in  SSL_OP_ALL, excess bits are ignored. Specifying
       0xFFFFFFFF disables all bug-workarounds on a 32-bit system. This should
       also  be  sufficient  on 64-bit systems, until OpenSSL abandons support
       for 32-bit systems and starts using  the  high  32  bits  of  a  64-bit
       bug-workaround mask.

       Otherwise,  the  parameter  is a white-space or comma separated list of
       specific named bug work-arounds chosen from the list below. It is  pos-
       sible  that  your  OpenSSL  version includes new bug work-arounds added
       after your Postfix source code was last updated, in that case  you  can
       only disable one of these via the hexadecimal syntax above.

       MICROSOFT_SESS_ID_BUG
              See SSL_CTX_set_options(3)

       NETSCAPE_CHALLENGE_BUG
              See SSL_CTX_set_options(3)

       LEGACY_SERVER_CONNECT
              See SSL_CTX_set_options(3)

       NETSCAPE_REUSE_CIPHER_CHANGE_BUG
              also   aliased  as  CVE-2010-4180.  Postfix  2.8  disables  this
              work-around by default with OpenSSL versions  that  may  predate
              the fix. Fixed in OpenSSL 0.9.8q and OpenSSL 1.0.0c.

       SSLREF2_REUSE_CERT_TYPE_BUG
              See SSL_CTX_set_options(3)

       MICROSOFT_BIG_SSLV3_BUFFER
              See SSL_CTX_set_options(3)

       MSIE_SSLV2_RSA_PADDING
              also   aliased  as  CVE-2005-2969.  Postfix  2.8  disables  this
              work-around by default with OpenSSL versions  that  may  predate
              the fix. Fixed in OpenSSL 0.9.7h and OpenSSL 0.9.8a.

       SSLEAY_080_CLIENT_DH_BUG
              See SSL_CTX_set_options(3)

       TLS_D5_BUG
              See SSL_CTX_set_options(3)

       TLS_BLOCK_PADDING_BUG
              See SSL_CTX_set_options(3)

       TLS_ROLLBACK_BUG
              See  SSL_CTX_set_options(3).   This is disabled in OpenSSL 0.9.7
              and later. Nobody should still be using 0.9.6!

       DONT_INSERT_EMPTY_FRAGMENTS
              See SSL_CTX_set_options(3)

       CRYPTOPRO_TLSEXT_BUG
              New with GOST support in OpenSSL 1.0.0.

       This feature is available in Postfix 2.8 and later.

tls_eecdh_strong_curve (default: prime256v1)
       The elliptic curve used by the Postfix SMTP server for sensibly  strong
       ephemeral  ECDH  key  exchange.  This curve is used by the Postfix SMTP
       server when "smtpd_tls_eecdh_grade  =  strong".  The  phrase  "sensibly
       strong"  means  approximately  128-bit  security  based  on  best known
       attacks. The selected curve must be implemented by OpenSSL (as reported
       by  ecparam(1) with the "-list_curves" option) and be one of the curves
       listed in Section 5.1.1 of RFC 4492. You should  not  generally  change
       this  setting.   Remote  SMTP  client implementations must support this
       curve for EECDH key exchange to take place.  It is unwise to choose  an
       "exotic" curve supported by only a small subset of clients.

       The  default  "strong"  curve  is  rated in NSA Suite B for information
       classified up to SECRET.

       Note: elliptic curve names are poorly standardized; different standards
       groups  are  assigning  different  names to the same underlying curves.
       The curve with the X9.62 name "prime256v1" is also known under the SECG
       name "secp256r1", but OpenSSL does not recognize the latter name.

       If  you  want  to  take maximal advantage of ciphers that offer forward
       secrecy see the Getting started section of FORWARD_SECRECY_README.  The
       full document conveniently presents all information about Postfix "per-
       fect" forward secrecy support in one place: what  forward  secrecy  is,
       how to tweak settings, and what you can expect to see when Postfix uses
       ciphers with forward secrecy.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 1.0.0 or later on platforms where EC algorithms
       have not been disabled by the vendor.

tls_eecdh_ultra_curve (default: secp384r1)
       The elliptic curve used by the Postfix SMTP server for maximally strong
       ephemeral  ECDH  key  exchange.  This curve is used by the Postfix SMTP
       server when "smtpd_tls_eecdh_grade  =  ultra".  The  phrase  "maximally
       strong"  means  approximately  192-bit  security  based  on  best known
       attacks.  This additional strength comes at a significant computational
       cost,  most  users should instead set "smtpd_tls_eecdh_grade = strong".
       The selected curve must be  implemented  by  OpenSSL  (as  reported  by
       ecparam(1)  with  the  "-list_curves"  option) and be one of the curves
       listed in Section 5.1.1 of RFC 4492. You should  not  generally  change
       this setting.

       This  default  "ultra"  curve  is  rated in NSA Suite B for information
       classified up to TOP SECRET.

       If you want to take maximal advantage of  ciphers  that  offer  forward
       secrecy see the Getting started section of FORWARD_SECRECY_README.  The
       full document conveniently presents all information about Postfix "per-
       fect"  forward  secrecy  support in one place: what forward secrecy is,
       how to tweak settings, and what you can expect to see when Postfix uses
       ciphers with forward secrecy.

       This feature is available in Postfix 2.6 and later, when it is compiled
       and linked with OpenSSL 1.0.0 or later on platforms where EC algorithms
       have not been disabled by the vendor.

tls_export_cipherlist (default: see postconf -d output)
       The  OpenSSL  cipherlist  for  "export"  or  higher grade ciphers. This
       defines the meaning  of  the  "export"  setting  in  smtpd_tls_ciphers,
       smtpd_tls_mandatory_ciphers,      smtp_tls_ciphers,     smtp_tls_manda-
       tory_ciphers, lmtp_tls_ciphers, and  lmtp_tls_mandatory_ciphers.   With
       Postfix  releases  before  the  middle  of  2015  this  is  the default
       cipherlist for the opportunistic ("may") TLS client security level  and
       also  the  default  cipherlist  for  the  SMTP server. You are strongly
       encouraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_high_cipherlist (default: see postconf -d output)
       The OpenSSL cipherlist for "high" grade ciphers. This defines the mean-
       ing  of  the  "high"  setting  in  smtpd_tls_ciphers,  smtpd_tls_manda-
       tory_ciphers,       smtp_tls_ciphers,       smtp_tls_mandatory_ciphers,
       lmtp_tls_ciphers,  and  lmtp_tls_mandatory_ciphers.  You  are  strongly
       encouraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_legacy_public_key_fingerprints (default: no)
       A temporary migration aid for sites  that  use  certificate  public-key
       fingerprints  with  Postfix  2.9.0..2.9.5, which use an incorrect algo-
       rithm. This parameter has no effect on the certificate fingerprint sup-
       port that is available since Postfix 2.2.

       Specify "tls_legacy_public_key_fingerprints = yes" temporarily, pending
       a  migration  from   configuration   files   with   incorrect   Postfix
       2.9.0..2.9.5  certificate public-key finger prints, to the correct fin-
       gerprints used by Postfix 2.9.6 and later.  To compute the correct cer-
       tificate public-key fingerprints, see TLS_README.

       This feature is available in Postfix 2.9.6 and later.

tls_low_cipherlist (default: see postconf -d output)
       The  OpenSSL cipherlist for "low" or higher grade ciphers. This defines
       the meaning of the "low" setting in smtpd_tls_ciphers, smtpd_tls_manda-
       tory_ciphers,       smtp_tls_ciphers,       smtp_tls_mandatory_ciphers,
       lmtp_tls_ciphers,  and  lmtp_tls_mandatory_ciphers.  You  are  strongly
       encouraged to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_medium_cipherlist (default: see postconf -d output)
       The  OpenSSL  cipherlist  for  "medium"  or  higher grade ciphers. This
       defines the meaning  of  the  "medium"  setting  in  smtpd_tls_ciphers,
       smtpd_tls_mandatory_ciphers,      smtp_tls_ciphers,     smtp_tls_manda-
       tory_ciphers, lmtp_tls_ciphers, and  lmtp_tls_mandatory_ciphers.   This
       is  the  default  cipherlist  for  mandatory  TLS encryption in the TLS
       client (with anonymous ciphers disabled when verifying server  certifi-
       cates).   This  is  the  default  cipherlist for opportunistic TLS with
       Postfix releases after the middle of 2015.  You are strongly encouraged
       to not change this setting.

       This feature is available in Postfix 2.3 and later.

tls_null_cipherlist (default: eNULL:!aNULL)
       The  OpenSSL cipherlist for "NULL" grade ciphers that provide authenti-
       cation without encryption. This defines the meaning of the "null"  set-
       ting  in  smtpd_mandatory_tls_ciphers,  smtp_tls_mandatory_ciphers  and
       lmtp_tls_mandatory_ciphers.  You are strongly encouraged to not  change
       this setting.

       This feature is available in Postfix 2.3 and later.

tls_preempt_cipherlist (default: no)
       With  SSLv3  and later, use the Postfix SMTP server's cipher preference
       order instead of the remote client's cipher preference order.

       By default, the OpenSSL server  selects  the  client's  most  preferred
       cipher  that  the server supports. With SSLv3 and later, the server may
       choose its own most preferred cipher that is supported (offered) by the
       client.  Setting  "tls_preempt_cipherlist  = yes" enables server cipher
       preferences.

       While server cipher selection may in some cases lead to a  more  secure
       or  performant  cipher  choice,  there is some risk of interoperability
       issues. In the past,  some  SSL  clients  have  listed  lower  priority
       ciphers  that they did not implement correctly. If the server chooses a
       cipher that the client prefers less,  it  may  select  a  cipher  whose
       client  implementation  is  flawed. Most notably Windows 2003 Microsoft
       Exchange servers have flawed  implementations  of  DES-CBC3-SHA,  which
       OpenSSL  considers stronger than RC4-SHA.  Enabling server cipher-suite
       selection  may  create  interoperability  issues  with   Windows   2003
       Microsoft Exchange clients.

       This feature is available in Postfix 2.8 and later, in combination with
       OpenSSL 0.9.7 and later.

tls_random_bytes (default: 32)
       The number of bytes that tlsmgr(8) reads from  $tls_random_source  when
       (re)seeding  the  in-memory pseudo random number generator (PRNG) pool.
       The default of 32 bytes (256 bits) is good enough for 128bit  symmetric
       keys.  If using EGD or a device file, a maximum of 255 bytes is read.

       This feature is available in Postfix 2.2 and later.

tls_random_exchange_name (default: see postconf -d output)
       Name  of  the  pseudo random number generator (PRNG) state file that is
       maintained by tlsmgr(8). The file is created when it  does  not  exist,
       and its length is fixed at 1024 bytes.

       As  of version 2.5, Postfix no longer uses root privileges when opening
       this file, and the  default  file  location  was  changed  from  ${con-
       fig_directory}/prng_exch  to  ${data_directory}/prng_exch.  As a migra-
       tion aid, an attempt to open the file under a non-Postfix directory  is
       redirected  to  the  Postfix-owned  data_directory,  and  a  warning is
       logged.

       This feature is available in Postfix 2.2 and later.

tls_random_prng_update_period (default: 3600s)
       The time between attempts by tlsmgr(8) to save the state of the  pseudo
       random  number  generator  (PRNG)  to the file specified with $tls_ran-
       dom_exchange_name.

       This feature is available in Postfix 2.2 and later.

tls_random_reseed_period (default: 3600s)
       The maximal time between attempts by tlsmgr(8) to re-seed the in-memory
       pseudo  random number generator (PRNG) pool from external sources.  The
       actual time between re-seeding attempts is calculated using  the  PRNG,
       and is between 0 and the time specified.

       This feature is available in Postfix 2.2 and later.

tls_random_source (default: see postconf -d output)
       The  external  entropy source for the in-memory tlsmgr(8) pseudo random
       number generator (PRNG) pool. Be sure to specify a non-blocking source.
       If  this  source is not a regular file, the entropy source type must be
       prepended:  egd:/path/to/egd_socket for a source  with  EGD  compatible
       socket interface, or dev:/path/to/device for a device file.

       Note:  on  OpenBSD systems specify /dev/arandom when /dev/urandom gives
       timeout errors.

       This feature is available in Postfix 2.2 and later.

tls_session_ticket_cipher (default: Postfix >=  3.0:  aes-256-cbc,  Postfix  <
       3.0: aes-128-cbc)
       Algorithm  used to encrypt RFC5077 TLS session tickets.  This algorithm
       must use CBC mode, have a 128-bit block  size,  and  must  have  a  key
       length between 128 and 256 bits.  The default is aes-256-cbc.  Overrid-
       ing the default to choose a different algorithm is discouraged.

       Setting this parameter empty disables session  ticket  support  in  the
       Postfix  SMTP server.  Another way to disable session ticket support is
       via the tls_ssl_options parameter.

       This feature is available in Postfix 3.0 and later.

tls_ssl_options (default: empty)
       List or bit-mask of OpenSSL options to enable.

       The OpenSSL toolkit provides a set of  options  that  applications  can
       enable to tune the OpenSSL behavior.  Some of these work around bugs in
       other implementations and are on by default.  You can use the  tls_dis-
       able_workarounds  parameter  to  selectively disable some or all of the
       bug work-arounds, making OpenSSL more strict at the cost of  non-inter-
       operability with SSL clients or servers that exhibit the bugs.

       Other  options are off by default, and typically enable or disable fea-
       tures rather than bug work-arounds.  These may be turned on (with care)
       via the tls_ssl_options parameter.  The value is a white-space or comma
       separated list of named options chosen from the list below.  The  names
       are  not  case-sensitive,  you  can  use lower-case if you prefer.  The
       upper case values below match the corresponding macro name in the ssl.h
       header  file with the SSL_OP_ prefix removed.  It is possible that your
       OpenSSL version includes new options added after  your  Postfix  source
       code  was  last  updated, in that case you can only enable one of these
       via the hexadecimal syntax below.

       You should only enable features via the hexadecimal mask when the  need
       to control the feature is critical (to deal with a new vulnerability or
       a serious interoperability problem).  Postfix DOES  NOT  promise  back-
       wards  compatible  behavior  with  respect to the mask bits.  A feature
       enabled via the mask in one release may be enabled by other means in  a
       later  release,  and the mask bit will then be ignored.  Therefore, use
       of the hexadecimal mask is only a temporary measure until a new Postfix
       or OpenSSL release provides a better solution.

       If  the  value  of the parameter is a hexadecimal long integer starting
       with "0x", the options corresponding to the bits specified in its value
       are  enabled  (see  openssl/ssl.h and SSL_CTX_set_options(3)).  You can
       only enable options not already controlled by other  Postfix  settings.
       For example, you cannot disable protocols or enable server cipher pref-
       erence.  Do not attempt to turn all features by specifying  0xFFFFFFFF,
       this is unlikely to be a good idea.

       LEGACY_SERVER_CONNECT
              See SSL_CTX_set_options(3).

       NO_TICKET
              See SSL_CTX_set_options(3).

       NO_COMPRESSION
              Disable  SSL  compression  even  if  supported  by  the  OpenSSL
              library.  Compression is CPU-intensive, and  compression  before
              encryption does not always improve security.

       This feature is available in Postfix 2.11 and later.

tls_wildcard_matches_multiple_labels (default: yes)
       Match multiple DNS labels with "*" in wildcard certificates.

       Some  mail service providers prepend the customer domain name to a base
       domain for which they have a wildcard TLS  certificate.   For  example,
       the MX records for example.com hosted by example.net may be:

           example.com. IN MX 0 example.com.mx1.example.net.
           example.com. IN MX 0 example.com.mx2.example.net.

       and the TLS certificate may be for "*.example.net". The "*" then corre-
       sponds with multiple labels in the  mail  server  domain  name.   While
       multi-label  wildcards are not widely supported, and are not blessed by
       any standard, there is little to be gained by disallowing their use  in
       this context.

       Notes:

             In  a  certificate name, the "*" is special only when it is used
              as the first label.

             While Postfix (2.11 or later) can match "*" with multiple domain
              name labels, other implementations likely will not.

             Earlier   Postfix   implementations   behave  as  if  "tls_wild-
              card_matches_multiple_labels = no".

       This feature is available in Postfix 2.11 and later.

tlsmgr_service_name (default: tlsmgr)
       The name of the tlsmgr(8) service  entry  in  master.cf.  This  service
       maintains TLS session caches and other information in support of TLS.

       This feature is available in Postfix 2.11 and later.

tlsproxy_enforce_tls (default: $smtpd_enforce_tls)
       Mandatory  TLS:  announce  STARTTLS support to remote SMTP clients, and
       require that clients use TLS encryption. See smtpd_enforce_tls for fur-
       ther details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_service_name (default: tlsproxy)
       The  name  of  the tlsproxy(8) service entry in master.cf. This service
       performs plaintext <=> TLS ciphertext conversion.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_CAfile (default: $smtpd_tls_CAfile)
       A file containing (PEM format) CA certificates of root CAs  trusted  to
       sign either remote SMTP client certificates or intermediate CA certifi-
       cates.  See smtpd_tls_CAfile for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_CApath (default: $smtpd_tls_CApath)
       A directory containing (PEM format) CA certificates of root CAs trusted
       to  sign either remote SMTP client certificates or intermediate CA cer-
       tificates. See smtpd_tls_CApath for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_always_issue_session_ids  (default:  $smtpd_tls_always_issue_ses-
       sion_ids)
       Force  the  Postfix  tlsproxy(8) server to issue a TLS session id, even
       when TLS session caching is turned off. See smtpd_tls_always_issue_ses-
       sion_ids for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ask_ccert (default: $smtpd_tls_ask_ccert)
       Ask   a   remote   SMTP   client   for   a   client   certificate.  See
       smtpd_tls_ask_ccert for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ccert_verifydepth (default: $smtpd_tls_ccert_verifydepth)
       The verification depth for remote SMTP client certificates. A depth  of
       1  is  sufficient  if  the issuing CA is listed in a local CA file. See
       smtpd_tls_ccert_verifydepth for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_cert_file (default: $smtpd_tls_cert_file)
       File with the Postfix tlsproxy(8) server RSA certificate in PEM format.
       This  file  may also contain the Postfix tlsproxy(8) server private RSA
       key.  See smtpd_tls_cert_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_ciphers (default: $smtpd_tls_ciphers)
       The minimum TLS cipher grade that the Postfix tlsproxy(8)  server  will
       use  with  opportunistic TLS encryption. See smtpd_tls_ciphers for fur-
       ther details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dcert_file (default: $smtpd_tls_dcert_file)
       File with the Postfix tlsproxy(8) server DSA certificate in PEM format.
       This  file  may also contain the Postfix tlsproxy(8) server private DSA
       key.  See smtpd_tls_dcert_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dh1024_param_file (default: $smtpd_tls_dh1024_param_file)
       File with DH parameters that the Postfix tlsproxy(8) server should  use
       with  non-export  EDH ciphers. See smtpd_tls_dh1024_param_file for fur-
       ther details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dh512_param_file (default: $smtpd_tls_dh512_param_file)
       File with DH parameters that the Postfix tlsproxy(8) server should  use
       with  export-grade EDH ciphers. See smtpd_tls_dh512_param_file for fur-
       ther details.  The default SMTP server cipher grade  is  "medium"  with
       Postfix releases after the middle of 2015, and as a result export-grade
       cipher suites are by default not used.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_dkey_file (default: $smtpd_tls_dkey_file)
       File with the Postfix tlsproxy(8) server DSA private key in PEM format.
       This  file may be combined with the Postfix tlsproxy(8) server DSA cer-
       tificate    file    specified    with    $smtpd_tls_dcert_file.     See
       smtpd_tls_dkey_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eccert_file (default: $smtpd_tls_eccert_file)
       File  with the Postfix tlsproxy(8) server ECDSA certificate in PEM for-
       mat.  This file may also contain the Postfix tlsproxy(8) server private
       ECDSA key.  See smtpd_tls_eccert_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eckey_file (default: $smtpd_tls_eckey_file)
       File  with the Postfix tlsproxy(8) server ECDSA private key in PEM for-
       mat.  This file may be combined with  the  Postfix  tlsproxy(8)  server
       ECDSA  certificate  file  specified  with  $smtpd_tls_eccert_file.  See
       smtpd_tls_eckey_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_eecdh_grade (default: $smtpd_tls_eecdh_grade)
       The Postfix tlsproxy(8) server  security  grade  for  ephemeral  ellip-
       tic-curve      Diffie-Hellman     (EECDH)     key     exchange.     See
       smtpd_tls_eecdh_grade for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_exclude_ciphers (default: $smtpd_tls_exclude_ciphers)
       List of ciphers or cipher types to exclude from the tlsproxy(8)  server
       cipher  list  at all TLS security levels. See smtpd_tls_exclude_ciphers
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_fingerprint_digest (default: $smtpd_tls_fingerprint_digest)
       The message digest algorithm to construct remote  SMTP  client-certifi-
       cate   fingerprints.   See   smtpd_tls_fingerprint_digest  for  further
       details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_key_file (default: $smtpd_tls_key_file)
       File with the Postfix tlsproxy(8) server RSA private key in PEM format.
       This  file may be combined with the Postfix tlsproxy(8) server RSA cer-
       tificate    file    specified    with    $smtpd_tls_cert_file.      See
       smtpd_tls_key_file for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_loglevel (default: $smtpd_tls_loglevel)
       Enable  additional  Postfix tlsproxy(8) server logging of TLS activity.
       Each logging level also includes the information that is  logged  at  a
       lower logging level. See smtpd_tls_loglevel for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_ciphers (default: $smtpd_tls_mandatory_ciphers)
       The  minimum  TLS cipher grade that the Postfix tlsproxy(8) server will
       use with mandatory TLS encryption. See smtpd_tls_mandatory_ciphers  for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_exclude_ciphers       (default:       $smtpd_tls_manda-
       tory_exclude_ciphers)
       Additional list  of  ciphers  or  cipher  types  to  exclude  from  the
       tlsproxy(8)  server  cipher list at mandatory TLS security levels.  See
       smtpd_tls_mandatory_exclude_ciphers for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_mandatory_protocols (default: $smtpd_tls_mandatory_protocols)
       The SSL/TLS protocols accepted by the Postfix tlsproxy(8)  server  with
       mandatory TLS encryption. If the list is empty, the server supports all
       available SSL/TLS protocol versions.  See smtpd_tls_mandatory_protocols
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_protocols (default: $smtpd_tls_protocols)
       List  of TLS protocols that the Postfix tlsproxy(8) server will exclude
       or include with opportunistic TLS encryption.  See  smtpd_tls_protocols
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_req_ccert (default: $smtpd_tls_req_ccert)
       With  mandatory  TLS  encryption,  require a trusted remote SMTP client
       certificate  in  order  to  allow  TLS  connections  to  proceed.   See
       smtpd_tls_req_ccert for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_security_level (default: $smtpd_tls_security_level)
       The  SMTP TLS security level for the Postfix tlsproxy(8) server; when a
       non-empty value is specified, this overrides  the  obsolete  parameters
       smtpd_use_tls  and  smtpd_enforce_tls. See smtpd_tls_security_level for
       further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_tls_session_cache_timeout (default: $smtpd_tls_session_cache_timeout)

       Obsolete  expiration  time  of  Postfix  tlsproxy(8) server TLS session
       cache information. Since the cache is shared with smtpd(8) and  managed
       by  tlsmgr(8),  there  is  only one expiration time for the SMTP server
       cache   shared   by   all   three   services,   namely   smtpd_tls_ses-
       sion_cache_timeout.

       This feature is available in Postfix 2.8 and later.

tlsproxy_use_tls (default: $smtpd_use_tls)
       Opportunistic  TLS:  announce  STARTTLS support to remote SMTP clients,
       but do not require that clients use TLS encryption.  See  smtpd_use_tls
       for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_watchdog_timeout (default: 10s)
       How much time a tlsproxy(8) process may take to process local or remote
       I/O before it is terminated by a built-in watchdog timer.   This  is  a
       safety mechanism that prevents tlsproxy(8) from becoming non-responsive
       due to a bug in Postfix itself or in system software.  To  avoid  false
       alarms  and unnecessary cache corruption this limit cannot be set under
       10s.

       Specify a non-zero time value  (an  integral  value  plus  an  optional
       one-letter  suffix  that specifies the time unit).  Time units: s (sec-
       onds), m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

trace_service_name (default: trace)
       The name of the trace service.  This  service  is  implemented  by  the
       bounce(8) daemon and maintains a record of mail deliveries and produces
       a mail delivery report when verbose delivery is requested  with  "send-
       mail -v".

       This feature is available in Postfix 2.1 and later.

transport_delivery_slot_cost (default: $default_delivery_slot_cost)
       A transport-specific override for the default_delivery_slot_cost param-
       eter value, where transport is the master.cf name of the message deliv-
       ery transport.

       Note:  transport_delivery_slot_cost  parameters  will  not  show  up in
       "postconf" command output before Postfix version 2.9.  This  limitation
       applies  to  many parameters whose name is a combination of a master.cf
       service  name  and  a  built-in  suffix   (in   this   case:   "_deliv-
       ery_slot_cost").

transport_delivery_slot_discount (default: $default_delivery_slot_discount)
       A  transport-specific  override  for the default_delivery_slot_discount
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       Note:  transport_delivery_slot_discount  parameters will not show up in
       "postconf" command output before Postfix version 2.9.  This  limitation
       applies  to  many parameters whose name is a combination of a master.cf
       service name and a built-in suffix (in this case:  "_delivery_slot_dis-
       count").

transport_delivery_slot_loan (default: $default_delivery_slot_loan)
       A transport-specific override for the default_delivery_slot_loan param-
       eter value, where transport is the master.cf name of the message deliv-
       ery transport.

       Note:  transport_delivery_slot_loan  parameters  will  not  show  up in
       "postconf" command output before Postfix version 2.9.  This  limitation
       applies  to  many parameters whose name is a combination of a master.cf
       service  name  and  a  built-in  suffix   (in   this   case:   "_deliv-
       ery_slot_loan").

transport_destination_concurrency_failed_cohort_limit  (default: $default_des-
       tination_concurrency_failed_cohort_limit)
       A  transport-specific  override  for  the   default_destination_concur-
       rency_failed_cohort_limit  parameter value, where transport is the mas-
       ter.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_failed_cohort_limit param-
       eters will not show up in "postconf" command output before Postfix ver-
       sion 2.9.  This limitation applies to many parameters whose name  is  a
       combination  of a master.cf service name and a built-in suffix (in this
       case: "_destination_concurrency_failed_cohort_limit").

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_limit (default: $default_destination_concur-
       rency_limit)
       A   transport-specific  override  for  the  default_destination_concur-
       rency_limit parameter value, where transport is the master.cf  name  of
       the message delivery transport.

       Note:  some transport_destination_concurrency_limit parameters will not
       show up in "postconf" command output before Postfix version 2.9.   This
       limitation  applies to many parameters whose name is a combination of a
       master.cf service name and a built-in suffix (in this case:  "_destina-
       tion_concurrency_limit").

transport_destination_concurrency_negative_feedback  (default: $default_desti-
       nation_concurrency_negative_feedback)
       A  transport-specific  override  for  the   default_destination_concur-
       rency_negative_feedback  parameter  value,  where transport is the mas-
       ter.cf name of the message delivery transport.

       Note: some transport_destination_concurrency_negative_feedback  parame-
       ters  will not show up in "postconf" command output before Postfix ver-
       sion 2.9.  This limitation applies to many parameters whose name  is  a
       combination  of a master.cf service name and a built-in suffix (in this
       case: "_destination_concurrency_negative_feedback").

       This feature is available in Postfix 2.5 and later.

transport_destination_concurrency_positive_feedback (default:  $default_desti-
       nation_concurrency_positive_feedback)
       A   transport-specific  override  for  the  default_destination_concur-
       rency_positive_feedback parameter value, where transport  is  the  mas-
       ter.cf name of the message delivery transport.

       Note:  some transport_destination_concurrency_positive_feedback parame-
       ters will not show up in "postconf" command output before Postfix  ver-
       sion  2.9.   This limitation applies to many parameters whose name is a
       combination of a master.cf service name and a built-in suffix (in  this
       case: "_destination_concurrency_positive_feedback").

       This feature is available in Postfix 2.5 and later.

transport_destination_rate_delay (default: $default_destination_rate_delay)
       A  transport-specific  override  for the default_destination_rate_delay
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       Note: some transport_destination_rate_delay parameters will not show up
       in "postconf" command output before Postfix version 2.9.  This  limita-
       tion  applies  to many parameters whose name is a combination of a mas-
       ter.cf service name and a built-in suffix  (in  this  case:  "_destina-
       tion_rate_delay").

       This feature is available in Postfix 2.5 and later.

transport_destination_recipient_limit  (default:  $default_destination_recipi-
       ent_limit)
       A  transport-specific  override  for  the   default_destination_recipi-
       ent_limit parameter value, where transport is the master.cf name of the
       message delivery transport.

       Note: some transport_destination_recipient_limit  parameters  will  not
       show  up in "postconf" command output before Postfix version 2.9.  This
       limitation applies to many parameters whose name is a combination of  a
       master.cf  service name and a built-in suffix (in this case: "_destina-
       tion_recipient_limit").

transport_extra_recipient_limit (default: $default_extra_recipient_limit)
       A transport-specific  override  for  the  default_extra_recipient_limit
       parameter  value,  where transport is the master.cf name of the message
       delivery transport.

       Note: transport_extra_recipient_limit parameters will not  show  up  in
       "postconf"  command output before Postfix version 2.9.  This limitation
       applies to many parameters whose name is a combination of  a  master.cf
       service  name  and  a  built-in  suffix  (in this case: "_extra_recipi-
       ent_limit").

transport_initial_destination_concurrency (default:  $initial_destination_con-
       currency)
       A  transport-specific  override for the initial_destination_concurrency
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       Note:  some  transport_initial_destination_concurrency  parameters will
       not show up in "postconf" command output before  Postfix  version  2.9.
       This  limitation applies to many parameters whose name is a combination
       of a master.cf service name and a built-in suffix (in this case: "_ini-
       tial_destination_concurrency").

       This feature is available in Postfix 2.5 and later.

transport_maps (default: empty)
       Optional lookup tables with mappings from recipient address to (message
       delivery  transport,  next-hop  destination).   See  transport(5)   for
       details.

       Specify  zero  or  more "type:table" lookup tables, separated by white-
       space or comma. Tables will be searched in the specified order until  a
       match is found.  If you use this feature with local files, run "postmap
       /etc/postfix/transport" after making a change.

       Pattern matching of domain names  is  controlled  by  the  presence  or
       absence  of  "transport_maps"  in  the parent_domain_matches_subdomains
       parameter value.

       For safety reasons, as of Postfix 2.3 this feature does not allow $num-
       ber substitutions in regular expression maps.

       Examples:

       transport_maps = dbm:/etc/postfix/transport
       transport_maps = hash:/etc/postfix/transport

transport_minimum_delivery_slots (default: $default_minimum_delivery_slots)
       A  transport-specific  override  for the default_minimum_delivery_slots
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       Note:  transport_minimum_delivery_slots  parameters will not show up in
       "postconf" command output before Postfix version 2.9.  This  limitation
       applies  to  many parameters whose name is a combination of a master.cf
       service name and a built-in  suffix  (in  this  case:  "_minimum_deliv-
       ery_slots").

transport_recipient_limit (default: $default_recipient_limit)
       A transport-specific override for the default_recipient_limit parameter
       value, where transport is the master.cf name of  the  message  delivery
       transport.

       Note:  some  transport_recipient_limit  parameters  will not show up in
       "postconf" command output before Postfix version 2.9.  This  limitation
       applies  to  many parameters whose name is a combination of a master.cf
       service name and a built-in suffix (in this case:  "_recipient_limit").

transport_recipient_refill_delay (default: $default_recipient_refill_delay)
       A  transport-specific  override  for the default_recipient_refill_delay
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       Note:  transport_recipient_refill_delay  parameters will not show up in
       "postconf" command output before Postfix version 2.9.  This  limitation
       applies  to  many parameters whose name is a combination of a master.cf
       service  name  and  a  built-in  suffix  (in   this   case:   "_recipi-
       ent_refill_delay").

       This feature is available in Postfix 2.4 and later.

transport_recipient_refill_limit (default: $default_recipient_refill_limit)
       A  transport-specific  override  for the default_recipient_refill_limit
       parameter value, where transport is the master.cf name of  the  message
       delivery transport.

       Note:  transport_recipient_refill_limit  parameters will not show up in
       "postconf" command output before Postfix version 2.9.  This  limitation
       applies  to  many parameters whose name is a combination of a master.cf
       service  name  and  a  built-in  suffix  (in   this   case:   "_recipi-
       ent_refill_limit").

       This feature is available in Postfix 2.4 and later.

transport_retry_time (default: 60s)
       The  time  between  attempts  by the Postfix queue manager to contact a
       malfunctioning message delivery transport.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

transport_time_limit (default: $command_time_limit)
       A  transport-specific  override  for  the  command_time_limit parameter
       value, where transport is the master.cf name of  the  message  delivery
       transport.

       Note:  transport_time_limit  parameters  will not show up in "postconf"
       command output before Postfix version 2.9.  This limitation applies  to
       many parameters whose name is a combination of a master.cf service name
       and a built-in suffix (in this case: "_time_limit").

transport_transport_rate_delay (default: $default_transport_rate_delay)
       A  transport-specific  override  for  the  default_transport_rate_delay
       parameter  value,  where the initial transport in the parameter name is
       the master.cf name of the message delivery transport.

trigger_timeout (default: 10s)
       The time limit for sending a trigger to a Postfix daemon (for  example,
       the  pickup(8)  or  qmgr(8)  daemon). This time limit prevents programs
       from getting stuck when the mail system is under heavy load.

       Time units: s (seconds), m (minutes), h (hours), d (days),  w  (weeks).
       The default time unit is s (seconds).

undisclosed_recipients_header (default: see postconf -d output)
       Message  header  that the Postfix cleanup(8) server inserts when a mes-
       sage contains no To: or Cc: message header. With Postfix 2.8 and later,
       the  default  value  is  empty.  With Postfix 2.4-2.7, specify an empty
       value to disable this feature.

       Example:

       # Default value before Postfix 2.8.
       # Note: the ":" and ";" are both required.
       undisclosed_recipients_header = To: undisclosed-recipients:;

unknown_address_reject_code (default: 450)
       The numerical response code when the  Postfix  SMTP  server  rejects  a
       sender or recipient address because its domain is unknown.  This is one
       of     the     possible     replies     from      the      restrictions
       reject_unknown_sender_domain and reject_unknown_recipient_domain.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

unknown_address_tempfail_action (default: $reject_tempfail_action)
       The Postfix SMTP server's action when  reject_unknown_sender_domain  or
       reject_unknown_recipient_domain  fail  due  to a temporary error condi-
       tion. Specify "defer" to defer the remote SMTP client  request  immedi-
       ately.  With  the  default  "defer_if_permit"  action, the Postfix SMTP
       server continues to look for opportunities to reject mail,  and  defers
       the client request only if it would otherwise be accepted.

       This feature is available in Postfix 2.6 and later.

unknown_client_reject_code (default: 450)
       The  numerical  Postfix SMTP server response code when a client without
       valid   address   <=>    name    mapping    is    rejected    by    the
       reject_unknown_client_hostname  restriction.  The  SMTP  server  always
       replies with 450 when the mapping failed due to a temporary error  con-
       dition.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

unknown_helo_hostname_tempfail_action (default: $reject_tempfail_action)
       The Postfix  SMTP  server's  action  when  reject_unknown_helo_hostname
       fails due to an temporary error condition. Specify "defer" to defer the
       remote SMTP client request immediately. With the default "defer_if_per-
       mit"  action,  the Postfix SMTP server continues to look for opportuni-
       ties to reject mail, and defers the client request  only  if  it  would
       otherwise be accepted.

       This feature is available in Postfix 2.6 and later.

unknown_hostname_reject_code (default: 450)
       The numerical Postfix SMTP server response code when the hostname spec-
       ified  with  the  HELO   or   EHLO   command   is   rejected   by   the
       reject_unknown_helo_hostname restriction.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

unknown_local_recipient_reject_code (default: 550)
       The numerical Postfix  SMTP  server  response  code  when  a  recipient
       address  is local, and $local_recipient_maps specifies a list of lookup
       tables that does not match the recipient.  A recipient address is local
       when   its   domain   matches   $mydestination,   $proxy_interfaces  or
       $inet_interfaces.

       The default setting is 550 (reject mail) but it is safer  to  initially
       use  450  (try  again  later)  so  you  have  time  to find out if your
       local_recipient_maps settings are OK.

       Example:

       unknown_local_recipient_reject_code = 450

       This feature is available in Postfix 2.0 and later.

unknown_relay_recipient_reject_code (default: 550)
       The numerical Postfix SMTP server reply code when a  recipient  address
       matches  $relay_domains,  and  relay_recipient_maps specifies a list of
       lookup tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_alias_reject_code (default: 550)
       The Postfix SMTP server reply code when  a  recipient  address  matches
       $virtual_alias_domains,  and  $virtual_alias_maps  specifies  a list of
       lookup tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unknown_virtual_mailbox_reject_code (default: 550)
       The Postfix SMTP server reply code when  a  recipient  address  matches
       $virtual_mailbox_domains, and $virtual_mailbox_maps specifies a list of
       lookup tables that does not match the recipient address.

       This feature is available in Postfix 2.0 and later.

unverified_recipient_defer_code (default: 450)
       The numerical Postfix SMTP server response  when  a  recipient  address
       probe fails due to a temporary error condition.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

       This feature is available in Postfix 2.6 and later.

unverified_recipient_reject_code (default: 450)
       The  numerical Postfix SMTP server response when a recipient address is
       rejected by the reject_unverified_recipient restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

       This feature is available in Postfix 2.1 and later.

unverified_recipient_reject_reason (default: empty)
       The Postfix SMTP server's reply when rejecting mail with reject_unveri-
       fied_recipient.  Do  not  include  the  numeric  SMTP reply code or the
       enhanced status code. By default, the response includes actual  address
       verification details.

       Example:

       unverified_recipient_reject_reason = Recipient address lookup failed

       This feature is available in Postfix 2.6 and later.

unverified_recipient_tempfail_action (default: $reject_tempfail_action)
       The Postfix SMTP server's action when reject_unverified_recipient fails
       due to a temporary error condition. Specify "defer" to defer the remote
       SMTP  client  request  immediately.  With the default "defer_if_permit"
       action, the Postfix SMTP server continues to look for opportunities  to
       reject  mail,  and defers the client request only if it would otherwise
       be accepted.

       This feature is available in Postfix 2.6 and later.

unverified_sender_defer_code (default: 450)
       The numerical Postfix SMTP server response code when a  sender  address
       probe fails due to a temporary error condition.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do not change this unless you have  a  complete  understanding  of  RFC
       5321.

       This feature is available in Postfix 2.6 and later.

unverified_sender_reject_code (default: 450)
       The  numerical  Postfix  SMTP  server  response  code  when a recipient
       address is rejected by the reject_unverified_sender restriction.

       Unlike elsewhere in Postfix, you can specify 250 in order to accept the
       address anyway.

       Do  not  change  this  unless  you have a complete understanding of RFC
       5321.

       This feature is available in Postfix 2.1 and later.

unverified_sender_reject_reason (default: empty)
       The Postfix SMTP server's reply when rejecting mail with reject_unveri-
       fied_sender. Do not include the numeric SMTP reply code or the enhanced
       status code. By default, the response includes actual address verifica-
       tion details.

       Example:

       unverified_sender_reject_reason = Sender address lookup failed

       This feature is available in Postfix 2.6 and later.

unverified_sender_tempfail_action (default: $reject_tempfail_action)
       The  Postfix  SMTP  server's action when reject_unverified_sender fails
       due to a temporary error condition. Specify "defer" to defer the remote
       SMTP  client  request  immediately.  With the default "defer_if_permit"
       action, the Postfix SMTP server continues to look for opportunities  to
       reject  mail,  and defers the client request only if it would otherwise
       be accepted.

       This feature is available in Postfix 2.6 and later.

verp_delimiter_filter (default: -=+)
       The characters Postfix accepts as  VERP  delimiter  characters  on  the
       Postfix sendmail(1) command line and in SMTP commands.

       This feature is available in Postfix 1.1 and later.

virtual_alias_address_length_limit (default: 1000)
       The  maximal  length of an email address after virtual alias expansion.
       This stops virtual aliasing loops  that  increase  the  address  length
       exponentially.

       This feature is available in Postfix 3.0 and later.

virtual_alias_domains (default: $virtual_alias_maps)
       Postfix  is  final  destination for the specified list of virtual alias
       domains, that is, domains  for  which  all  addresses  are  aliased  to
       addresses  in  other local or remote domains. The SMTP server validates
       recipient addresses with $virtual_alias_maps and  rejects  non-existent
       recipients.   See   also   the   virtual  alias  domain  class  in  the
       ADDRESS_CLASS_README file

       This feature is available in Postfix 2.0 and later. The  default  value
       is backwards compatible with Postfix version 1.1.

       The  default  value  is  $virtual_alias_maps  so  that you can keep all
       information about virtual alias domains in one place.  If you have many
       users,  it  is  better  to  separate information that changes more fre-
       quently (virtual address ->  local  or  remote  address  mapping)  from
       information  that  changes  less frequently (the list of virtual domain
       names).

       Specify a list of host or domain names,  "/file/name"  or  "type:table"
       patterns, separated by commas and/or whitespace. A "/file/name" pattern
       is replaced by its contents; a "type:table"  lookup  table  is  matched
       when  a  table  entry  matches  a  lookup  string (the lookup result is
       ignored).  Continue long lines by starting the next  line  with  white-
       space.  Specify  "!pattern"  to  exclude a host or domain name from the
       list. The form "!/file/name" is supported only in Postfix  version  2.4
       and later.

       See also the VIRTUAL_README and ADDRESS_CLASS_README documents for fur-
       ther information.

       Example:

       virtual_alias_domains = virtual1.tld virtual2.tld

virtual_alias_expansion_limit (default: 1000)
       The maximal number of addresses that virtual alias  expansion  produces
       from each original recipient.

       This feature is available in Postfix 2.1 and later.

virtual_alias_maps (default: $virtual_maps)
       Optional lookup tables that alias specific mail addresses or domains to
       other local or remote address.  The table format and lookups are  docu-
       mented  in virtual(5). For an overview of Postfix address manipulations
       see the ADDRESS_REWRITING_README document.

       This feature is available in Postfix 2.0 and later. The  default  value
       is backwards compatible with Postfix version 1.1.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.  Note: these lookups are recursive.

       If  you  use  this  feature with indexed files, run "postmap /etc/post-
       fix/virtual" after changing the file.

       Examples:

       virtual_alias_maps = dbm:/etc/postfix/virtual
       virtual_alias_maps = hash:/etc/postfix/virtual

virtual_alias_recursion_limit (default: 1000)
       The maximal nesting depth of virtual alias  expansion.   Currently  the
       recursion  limit  is  applied  only to the left branch of the expansion
       graph, so the depth of the tree can in the worst case reach the sum  of
       the expansion and recursion limits.  This may change in the future.

       This feature is available in Postfix 2.1 and later.

virtual_delivery_status_filter (default: $default_delivery_status_filter)
       Optional  filter for the virtual(8) delivery agent to change the deliv-
       ery status code or  explanatory  text  of  successful  or  unsuccessful
       deliveries.  See default_delivery_status_filter for details.

       This feature is available in Postfix 3.0 and later.

virtual_destination_concurrency_limit  (default:  $default_destination_concur-
       rency_limit)
       The maximal number of parallel deliveries to the same  destination  via
       the  virtual  message delivery transport. This limit is enforced by the
       queue manager. The message delivery transport name is the  first  field
       in the entry in the master.cf file.

virtual_destination_recipient_limit   (default:   $default_destination_recipi-
       ent_limit)
       The maximal number of recipients per message for  the  virtual  message
       delivery  transport.  This  limit is enforced by the queue manager. The
       message delivery transport name is the first field in the entry in  the
       master.cf file.

       Setting  this  parameter  to  a  value of 1 changes the meaning of vir-
       tual_destination_concurrency_limit from  concurrency  per  domain  into
       concurrency per recipient.

virtual_gid_maps (default: empty)
       Lookup  tables  with  the per-recipient group ID for virtual(8) mailbox
       delivery.

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       In a lookup table, specify a left-hand side of "@domain.tld"  to  match
       any  user  in  the  specified  domain  that  does  not  have a specific
       "user@domain.tld" entry.

       When  a  recipient  address   has   an   optional   address   extension
       (user+foo@domain.tld),  the virtual(8) delivery agent looks up the full
       address first, and when the lookup fails, it looks  up  the  unextended
       address (user@domain.tld).

       Note  1:  for security reasons, the virtual(8) delivery agent disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note  2:  for  security  reasons,  the  virtual(8)  delivery agent will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open  the  table  directly.  Before Postfix version 2.2, the virtual(8)
       delivery agent will terminate with a fatal error.

virtual_mailbox_base (default: empty)
       A prefix that the virtual(8) delivery agent prepends  to  all  pathname
       results  from  $virtual_mailbox_maps  table  lookups.  This is a safety
       measure to ensure that an out of control map doesn't  litter  the  file
       system with mailboxes.  While virtual_mailbox_base could be set to "/",
       this setting isn't recommended.

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

       Example:

       virtual_mailbox_base = /var/mail

virtual_mailbox_domains (default: $virtual_mailbox_maps)
       Postfix is final destination for the specified list of domains; mail is
       delivered  via  the  $virtual_transport  mail  delivery  transport.  By
       default this is the Postfix virtual(8) delivery agent.  The SMTP server
       validates  recipient  addresses  with $virtual_mailbox_maps and rejects
       mail for non-existent recipients.  See also the virtual mailbox  domain
       class in the ADDRESS_CLASS_README file.

       This  parameter expects the same syntax as the mydestination configura-
       tion parameter.

       This feature is available in Postfix 2.0 and later. The  default  value
       is backwards compatible with Postfix version 1.1.

virtual_mailbox_limit (default: 51200000)
       The  maximal  size  in  bytes  of  an  individual virtual(8) mailbox or
       maildir file, or zero (no limit).

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

virtual_mailbox_lock (default: see postconf -d output)
       How to lock a UNIX-style virtual(8) mailbox before attempting delivery.
       For  a  list  of  available file locking methods, use the "postconf -l"
       command.

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

       This setting is ignored  with  maildir  style  delivery,  because  such
       deliveries are safe without application-level locks.

       Note  1:  the dotlock method requires that the recipient UID or GID has
       write access to the parent directory of the recipient's mailbox file.

       Note 2: the default setting of this parameter is system dependent.

virtual_mailbox_maps (default: empty)
       Optional lookup tables with all valid addresses  in  the  domains  that
       match $virtual_mailbox_domains.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or comma. Tables will be searched in the specified order until a  match
       is found.

       In  a  lookup table, specify a left-hand side of "@domain.tld" to match
       any user in  the  specified  domain  that  does  not  have  a  specific
       "user@domain.tld" entry.

       The  remainder  of  this  text  is  specific to the virtual(8) delivery
       agent.  It does not apply when mail is delivered with a different  mail
       delivery program.

       The virtual(8) delivery agent uses this table to look up the per-recip-
       ient mailbox or maildir pathname.  If the lookup result ends in a slash
       ("/"),  maildir-style  delivery  is  carried out, otherwise the path is
       assumed to specify a UNIX-style mailbox file.  Note that $virtual_mail-
       box_base is unconditionally prepended to this path.

       When   a   recipient   address   has   an  optional  address  extension
       (user+foo@domain.tld), the virtual(8) delivery agent looks up the  full
       address  first,  and  when the lookup fails, it looks up the unextended
       address (user@domain.tld).

       Note 1: for security reasons, the virtual(8) delivery  agent  disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note 2: for  security  reasons,  the  virtual(8)  delivery  agent  will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open the table directly. Before Postfix  version  2.2,  the  virtual(8)
       delivery agent will terminate with a fatal error.

virtual_maps (default: empty)
       Optional lookup tables with a) names of domains for which all addresses
       are aliased to addresses in other  local  or  remote  domains,  and  b)
       addresses  that  are  aliased  to  addresses  in  other local or remote
       domains.  Available before Postfix version 2.0.  With  Postfix  version
       2.0   and   later,   this   is  replaced  by  separate  controls:  vir-
       tual_alias_domains and virtual_alias_maps.

virtual_minimum_uid (default: 100)
       The minimum user ID value that the virtual(8) delivery agent accepts as
       a  result  from  $virtual_uid_maps  table lookup.  Returned values less
       than this will be rejected, and the message will be deferred.

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

virtual_transport (default: virtual)
       The default mail delivery transport and next-hop destination for  final
       delivery  to domains listed with $virtual_mailbox_domains.  This infor-
       mation can be overruled with the transport(5) table.

       Specify a string of the form transport:nexthop, where transport is  the
       name  of  a mail delivery transport defined in master.cf.  The :nexthop
       destination is optional; its syntax is documented in the manual page of
       the corresponding delivery agent.

       This feature is available in Postfix 2.0 and later.

virtual_uid_maps (default: empty)
       Lookup tables with the per-recipient user ID that the virtual(8) deliv-
       ery agent uses while writing to the recipient's mailbox.

       This parameter is specific to the virtual(8) delivery agent.   It  does
       not  apply  when  mail is delivered with a different mail delivery pro-
       gram.

       Specify zero or more "type:name" lookup tables, separated by whitespace
       or  comma. Tables will be searched in the specified order until a match
       is found.

       In a lookup table, specify a left-hand side of "@domain.tld"  to  match
       any  user  in  the  specified  domain  that  does  not  have a specific
       "user@domain.tld" entry.

       When  a  recipient  address   has   an   optional   address   extension
       (user+foo@domain.tld),  the virtual(8) delivery agent looks up the full
       address first, and when the lookup fails, it looks  up  the  unextended
       address (user@domain.tld).

       Note  1:  for security reasons, the virtual(8) delivery agent disallows
       regular expression substitution of $1 etc. in regular expression lookup
       tables, because that would open a security hole.

       Note  2:  for  security  reasons,  the  virtual(8)  delivery agent will
       silently ignore requests to use the proxymap(8) server. Instead it will
       open  the  table  directly.  Before Postfix version 2.2, the virtual(8)
       delivery agent will terminate with a fatal error.

SEE ALSO
       postconf(1), Postfix configuration parameter maintenance
       master(5), Postfix daemon configuration maintenance

LICENSE
       The Secure Mailer license must be distributed with this software.

AUTHOR(S)
       Wietse Venema
       IBM T.J. Watson Research
       P.O. Box 704
       Yorktown Heights, NY 10598, USA

       Wietse Venema
       Google, Inc.
       111 8th Avenue
       New York, NY 10011, USA

       Viktor Dukhovni



                                                                   POSTCONF(5)

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