POSTCONF(5)                                                        POSTCONF(5)



NAME
       postconf - Postfix configuration parameters

SYNOPSIS
       postconf parameter ...

       postconf -e "parameter=value" ...

DESCRIPTION
       The  Postfix main.cf configuration file specifies a small subset of all
       the parameters that control the operation of the Postfix  mail  system.
       Parameters not specified in main.cf 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  "$name",  "${name}"  or  "$(name)"  are
                     recursively replaced by the value of the named parameter.

                    The  expression  "${name?value}"  expands to "value" when
                     "$name" is non-empty. This form is supported with Postfix
                     version 2.2 and later.

                    The  expression  "${name:value}"  expands to "value" when
                     "$name" is empty. This form  is  supported  with  Postfix
                     version 2.2 and later.

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

             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
       2821.

       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
       2821.

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_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_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.

       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: 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:

       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.

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

       Note: if mail to the BCC address bounces it will  be  returned  to  the
       sender.

       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: 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
       server's 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  SMTP clients are allowed to specify the XVERP command.  This com-
       mand 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)
       The maximal time a bounce message is queued  before  it  is  considered
       undeliverable.  By default, this is the same as the queue life time 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 truncated 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 inter-operability with 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.

       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 system-wide recipient address extension delimiter.

       ${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.

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.

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 corresponding
       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_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  par-
       ent_domain_matches_subdomains parameter.

       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.

       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_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; with per-destination recipient  limit  >
       1, a destination is a domain, otherwise it is a recipient.

       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 changes the meaning of the cor-
       responding  per-destination  concurrency  limit  from  concurrency  per
       domain into concurrency per 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  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_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
       2821.

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
       small delay values 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.

       This feature is enabled with the delay_warning_time parameter.

delay_warning_time (default: 0h)
       The time after which the sender receives the message  headers  of  mail
       that is still queued.

       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).

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.

       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

dnsblog_reply_delay (default: 0s)
       A debugging aid to artifically 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_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. The name=value form is supported with  Postfix  version
       2.1 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.

       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 system-wide recipient address extension delimiter.

       ${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.

       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. The name=value form is supported with  Postfix  version
       2.1 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 SMTP server process limit, "in_flow_delay = 1s"
       limits the mail inflow to 100 messages per second above the  number  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 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 problem 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: ipv4)
       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.

       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 to DNS type A record lookups, 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 attempt to connect via IPv6 before attempting to use IPv4.

       Examples:

       inet_protocols = ipv4 (DEFAULT)
       inet_protocols = all
       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  transport-
       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 Postfix-
       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
       2821.

ipc_idle (default: version dependent)
       The  time  after  which  a client closes an idle internal communication
       channel.  The purpose is to  allow  servers  to  terminate  voluntarily
       after  they  become  idle.  This  is  used, for example, by the 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  servers  to  terminate  voluntarily
       after  reaching  their client limit.  This is used, for example, by the
       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.

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_assume_final (default: no)
       When  an  LMTP  server announces no DSN support, assume that the server
       performs final delivery, and send "delivered" delivery status notifica-
       tions instead of "relayed". The default setting is backwards compatible
       to avoid the infinetisimal 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 LMTP servers in use, and the concurrency limit specified for the
       LMTP  client.  Cached connections are closed under any of the following
       conditions:

             The LMTP client idle time limit is reached.  This limit is spec-
              ified 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  LMTP  server
              associated with the current session does not respond to the RSET
              command.

       Most of these limitations will be removed after  Postfix  implements  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 LMTP 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 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_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 LMTP client time limit for sending the LMTP ".", and for  receiving
       the 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  LMTP  client time limit for sending the LMTP DATA command, and for
       receiving the 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  LMTP client time limit for sending the LMTP message content.  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_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  LMTP  client  will ignore in the LHLO response from a remote
       LMTP server. See lmtp_discard_lhlo_keywords for details. The  table  is
       not  indexed  by  hostname for consistency with smtpd_discard_ehlo_key-
       word_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  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_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_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_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 LMTP client time limit  for  sending  the  LHLO  command,  and  for
       receiving the initial 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  LMTP  client time limit for sending the MAIL FROM command, and for
       receiving the 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_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  LMTP  client  time  limit  for  sending  the QUIT command, and for
       receiving the 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  LMTP  client  time  limit for sending the RCPT TO command, and for
       receiving the 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 LMTP client time limit  for  sending  the  RSET  command,  and  for
       receiving  the  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 LMTP client lookup tables with one username:password entry per
       host  or  domain.   If a remote host or domain has no username: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_xforward_command (default: no)
       Send  an  XFORWARD command to the 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 supports  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: export)
       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_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: empty)
       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)
       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: empty)
       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_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  LMTP  client  time limit for sending the XFORWARD command, and for
       receiving the 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_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 client
              TLS certificate fingerprint  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 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.

       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 system-wide recipient address extension delimiter.

       $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 a user account that does not
       share a group with other accounts and that owns no other files or  pro-
       cesses  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/postfix/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  system-
       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.

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.

       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
       2821.

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:

       # 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)
       The maximal time a message is queued before it is sent back as undeliv-
       erable.

       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_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 \\.

       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 \\.

       Example:

       message_strip_characters = \0

       This feature is available in Postfix 2.3 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_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 param-
       eter 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
       2821.

       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" SMTP  clients  that  have  more  privileges  than
       "strangers".

       In particular, "trusted" SMTP clients are allowed to relay mail through
       Postfix.  See the smtpd_recipient_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:  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: 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"
              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"
              SMTP clients in the same IP class A/B/C networks  as  the  local
              machine.   Don't  do  this  with  a dialup site - it would cause
              Postfix to "trust" your  entire  provider's  network.   Instead,
              specify  an  explicit mynetworks list by hand, as described with
              the mynetworks configuration 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".  See the MILTER_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).

       delay  Send the postmaster copies of the headers of delayed  mail.  The
              notification   is   sent  to  the  address  specified  with  the
              delay_notice_recipient configuration parameter  (default:  post-
              master).

       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

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)
       What Postfix features match subdomains of  "domain.tld"  automatically,
       instead  of  requiring  an  explicit  ".domain.tld"  pattern.   This is
       planned backwards compatibility:  eventually, all Postfix features  are
       expected  to  require  explicit  ".domain.tld"  style patterns when you
       really want to match subdomains.

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.

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.

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.

        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

       /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 an 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 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
       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 (seconds),
       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 an SMTP client is  permanently
       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.

       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 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 proto-
       col 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: ${stress?10}${stress:300}s)
       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  an  SMTP  client's  combined
       DNSBL  score  is  equal to or greater than a threshold (as defined with
       the postscreen_dnsbl_sites and postscreen_dnsbl_threshold  parameters).
       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_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 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
              SMTP client's DNSBL score by 1.  Otherwise, the weight  must  be
              an  integral number, and postscreen(8) adds the specified weight
              to the SMTP client's DNSBL score.  Specify a negative 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 an SMTP client, based on its
       combined DNSBL score as defined with the postscreen_dnsbl_sites parame-
       ter.

       This feature is available in Postfix 2.8.

postscreen_dnsbl_ttl (default: 1h)
       The  amount  of time that postscreen(8) will use the result from a suc-
       cessful DNS blocklist 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 (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_enforce_tls (default: $smtpd_enforce_tls)
       Mandatory TLS: announce STARTTLS support to 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 an 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 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  (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

postscreen_greet_wait (default: ${stress?2}${stress:6}s)
       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 an 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 (seconds),
       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 an 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 (seconds),
       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  SMTP
       server process. When this queue is full, all clients will receive a 421
       reponse.

       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 SMTP server process.
       When this queue is full, all non-whitelisted clients will receive a 421
       reponse.

       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 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_use_tls (default: $smtpd_use_tls)
       Opportunistic  TLS:  announce  STARTTLS support to 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 an SMTP
       client command or to perform a cache operation before it is  terminated
       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 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 (seconds),
       m (minutes), h (hours), d (days), w (weeks).

       This feature is available in Postfix 2.8.

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.  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 size of the short-term, in-memory
       "dead" destination 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 clients are allowed to connect to the 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.

       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 QMQP server will pause before sending a negative reply  to
       the  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 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 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.

       This feature is available in Postfix 2.1 and later.

       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.

       Specify  the  types  and  names of databases to use.  After change, run
       "postmap /etc/postfix/recipient_bcc".

       Note: if mail to the BCC address bounces it will  be  returned  to  the
       sender.

       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

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 separator between user names  and  address  extensions  (user+foo).
       See canonical(5), local(8), relocated(5) and virtual(5) for the effects
       this has on aliases, canonical, virtual, relocated and on .forward file
       lookups.   Basically,  the  software  tries  user+foo  and .forward+foo
       before trying user and .forward.

       Example:

       recipient_delimiter = +

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
       2821.

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 for
       which  the  Postfix  SMTP  server  will  allow  access  with  the  per-
       mit_tls_clientcerts  feature.  The fingerprint digest algorithm is con-
       figurable via the smtpd_tls_fingerprint_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.

       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: $mydestination)
       What destination domains (and  subdomains  thereof)  this  system  will
       relay   mail  to.  Subdomain  matching  is  controlled  with  the  par-
       ent_domain_matches_subdomains parameter.  For  details  about  how  the
       relay_domains   value   is  used,  see  the  description  of  the  per-
       mit_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.

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
       2821.

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.

       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).

       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 tempo-
       rary 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  inter-operability  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.

       This feature is available in Postfix 2.1 and later.

       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.

       Specify  the  types  and  names of databases to use.  After change, run
       "postmap /etc/postfix/sender_bcc".

       Note: if mail to the BCC address bounces it will  be  returned  to  the
       sender.

       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

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.

       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.

       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_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".

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: ipv6)
       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.

       This feature is available in Postfix 2.8 and later.

smtp_always_send_ehlo (default: yes)
       Always send EHLO at the start of an SMTP session.

       With  "smtp_always_send_ehlo  =  no",  Postfix sends EHLO only when the
       word "ESMTP" appears  in  the  server  greeting  banner  (example:  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)
       Allow  DNS  CNAME  records  to override the servername that the Postfix
       SMTP client uses for logging, SASL password lookup,  TLS  policy  deci-
       sions,  or TLS certificate verification. The value "no" hardens Postfix
       smtp_tls_per_site hostname-based policies against false hostname infor-
       mation  in DNS CNAME records, and makes SASL password file lookups more
       predictable. This is the default setting as of Postfix 2.3.

       This feature is available in Postfix 2.2.9 and later.

smtp_connect_timeout (default: 30s)
       The 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_reuse_limit (default: 10)
       When SMTP connection caching is enabled, the number of  times  that  an
       SMTP session may be reused before it is closed.

       This feature is available in Postfix 2.2. In Postfix 2.3 it is replaced
       by $smtp_connection_reuse_time_limit.

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_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  SMTP client time limit for sending the SMTP ".", and for receiving
       the 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 SMTP client time limit for sending the SMTP DATA command,  and  for
       receiving the 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 SMTP client time limit for sending the SMTP message content.   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:  Postfix 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_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.

       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_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_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.

       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 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.

       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 EHLO or HELO 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 SMTP client time limit for sending the HELO or  EHLO  command,  and
       for receiving the initial 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).

       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: 990)
       The  maximal  length of message header and body lines that Postfix will
       send via SMTP.  Longer lines are broken by inserting "<CR><LF><SPACE>".
       This minimizes the damage to MIME formatted mail.

       By  default, the line length is limited to 990 characters, because some
       server implementations cannot receive mail with long lines.

smtp_mail_timeout (default: 300s)
       The SMTP client time limit for sending the MAIL FROM command,  and  for
       receiving the 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  mail exchanger lookups, or zero (no limit). Prior to Postfix ver-
       sion 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  giving
       up  or  delivering  to a fall-back relay host, or zero (no limit). This
       restriction ignores sessions that fail to  complete  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_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.

       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  SMTP  client  time  limit  for  sending  the QUIT command, and for
       receiving the 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 SMTP MAIL FROM and RCPT TO commands as required by
       RFC 2821. This includes putting quotes around an address localpart that
       ends in ".".

       The  default  is to comply with RFC 2821. 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 SMTP client time limit for sending the SMTP RCPT  TO  command,  and
       for receiving the 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 inter-operability 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.

       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 SMTP client time limit  for  sending  the  RSET  command,  and  for
       receiving  the  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  further  restricts  what server mechanisms the client will
       take into consideration.

       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 SMTP client lookup tables with one username:password entry per
       remote  hostname  or  domain,  or  sender address 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.

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_xforward_command (default: no)
       Send  the  non-standard  XFORWARD  command when the Postfix SMTP server
       EHLO response announces XFORWARD support.

       This allows an "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 localhost[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,  Postfix  moves  on  the  next  mail  exchanger.   Specify
       "smtp_skip_4xx_greeting  = no" if Postfix should defer delivery immedi-
       ately.

       This feature is available in Postfix 2.0 and  earlier.   Later  Postfix
       versions always skip SMTP servers that greet with a 4XX status code.

smtp_skip_5xx_greeting (default: yes)
       Skip  SMTP  servers  that greet with a 5XX status code (go away, do not
       try again later).

       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. The default setting is incorrect, but it is what a lot  of
       people expect to happen.

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 "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 certificate 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 "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  inter-operability  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: export)
       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  "export" ensures maximum
       inter-operability. Because encryption is  optional,  stronger  controls
       are  not appropriate, and this setting SHOULD NOT be changed unless the
       change is essential.

       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.

       Example:
       smtp_tls_ciphers = export

       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_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, certificate authorities are not used,
       and certificate expiration times are ignored. Instead, server  certifi-
       cates are verified directly via their "fingerprint". The fingerprint is
       a message digest of the server certificate.  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 fingerprint. The fingerprint is the mes-
       sage  digest  of  the  server certificate 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 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

       This feature is available in Postfix 2.5 and later.

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 TLS handshake and certificate information.

              2 Log levels during TLS negotiation.

              3 Log hexadecimal and ASCII dump of TLS negotiation process.

              4  Log hexadecimal and ASCII dump of complete transmission after
              STARTTLS.

       Use "smtp_tls_loglevel = 3" only in case of problems. 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.   This  is  the
              default  for opportunistic encryption. It is not recommended for
              mandatory encryption unless you must enforce TLS with "crippled"
              peers.   The   underlying   cipherlist   is  specified  via  the
              tls_export_cipherlist configuration  parameter,  which  you  are
              strongly encouraged to not change.

       low    Enable  "LOW"  grade or better OpenSSL ciphers.  This setting is
              only appropriate for  internal  mail  servers.   The  underlying
              cipherlist is specified via the tls_low_cipherlist configuration
              parameter, which you are strongly encouraged to not change.

       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  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)
       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".

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1"  and
       "TLSv1.2".  If an older Postfix version is linked against OpenSSL 1.0.1
       or later, these, or any other new protocol versions,  are  uncondition-
       ally enabled.

       With  Postfix >= 2.5 the parameter syntax is expanded to support proto-
       col exclusions.  One  can  now  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 supported,
       but not recommended. The exclusion form more closely matches the behav-
       iour when the OpenSSL library is newer than Postfix.

       Since  SSL  version  2  has known protocol weaknesses and is now depre-
       cated, the default  setting  excludes  "SSLv2".   This  means  that  by
       default, SSL version 2 will not be used at the "encrypt" security level
       and higher.

       See  the  documentation  of  the  smtp_tls_policy_maps  parameter   and
       TLS_README for more information about security levels.

       Example:

       # Preferred form with Postfix >= 2.5:
       smtp_tls_mandatory_protocols = !SSLv2, !SSLv3
       # Alternative form.
       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.

       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
              inter-operability. 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.

       fingerprint
              Certificate fingerprint verification. Available with Postfix 2.5
              and later. At this security level, there are no trusted certifi-
              cate  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 valid "fingerprints" of the  server  certificate.  The
              digest  algorithm  used to calculate the fingerprint is selected
              by the smtp_tls_fingerprint_digest parameter.  Multiple  finger-
              prints  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)
       List  of  TLS  protocols  that  the Postfix SMTP client will exclude or
       include with opportunistic TLS encryption. Starting with  Postfix  2.6,
       the Postfix SMTP client will by default not use the obsolete SSLv2 pro-
       tocol.

       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".

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1"  and
       "TLSv1.2".  If an older Postfix version is linked against OpenSSL 1.0.1
       or later, these, or any other new protocol versions,  are  uncondition-
       ally enabled.

       To  include  a  protocol  list its name, to exclude it, prefix the name
       with a "!" character. To exclude SSLv2 even 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  behaviour
       when the OpenSSL library is newer than Postfix.

       Example:
       # TLSv1 only!
       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)
       The server certificate peername verification method  for  the  "secure"
       TLS  security  level.  In  a  "secure" TLS policy table ($smtp_tls_pol-
       icy_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   TLS  will  not  be used unless enabled for specific destinations
              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  inter-operability.   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.

       fingerprint
              Certificate fingerprint verification. Available with Postfix 2.5
              and later. At this security level, there are no trusted certifi-
              cate authorities. The certificate trust chain, expiration  date,
              ...    are    not   checked.   Instead,   the   smtp_tls_finger-
              print_cert_match parameter lists the valid "fingerprints" of the
              server  certificate.  The digest algorithm used to calculate the
              fingerprint  is  selected  by  the   smtp_tls_fingerprint_digest
              parameter.

       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

       # 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.

       This feature is available in Postfix 2.2 and later.

smtp_tls_verify_cert_match (default: hostname)
       The  server  certificate  peername verification method for the "verify"
       TLS security level. In a  "verify"  TLS  policy  table  ($smtp_tls_pol-
       icy_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_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 SMTP client time limit for sending the XFORWARD  command,  and  for
       receiving the 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 SMTP clients are allowed to specify the XVERP command.  This  com-
       mand 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 SMTP clients are allowed to use the XCLIENT feature.  This command
       overrides SMTP client information that is used for access control. Typ-
       ical use is for SMTP-based content filters, fetchmail-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  SMTP  clients are allowed to use the XFORWARD feature.  This com-
       mand 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_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.

       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  SMTP  server  access  restrictions in the context of a client
       SMTP connection request.   See  SMTPD_ACCESS_README,  section  "Delayed
       evaluation of SMTP access restriction lists" for a discussion of evalu-
       ation 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 client certificate fingerprint as  lookup  key  for  the
              specified  access(5)  database;  with  Postfix version 2.2, also
              require that the SMTP client certificate  is  verified  success-
              fully.  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_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_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.

       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 system-
              supplied default CAs.  This feature is  available  with  Postfix
              version 2.2.

       permit_tls_clientcerts
              Permit  the request when the remote SMTP client certificate fin-
              gerprint  is  listed  in  $relay_clientcerts.   The  fingerprint
              digest  algorithm  is  configurable  via  the  smtpd_tls_finger-
              print_digest parameter (hard-coded as md5 prior to Postfix  ver-
              sion  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
              EHLO or HELO 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
              Change  the  meaning  of the next restriction, so that it logs a
              warning instead of rejecting a request (look for logfile records
              that  contain  "reject_warning"). This is useful for testing new
              restrictions in a "live" environment without risking unnecessary
              loss of mail.

       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  inter-oper-
       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:]]+)'>(.*)/     RCPT TO:<$1>$2

           # Bounce-never mail sink. Use notify_classes=bounce,resource,software
           # to send bounced mail to the postmaster (with message body removed).
           /^(RCPT\s+TO:.*?)\bNOTIFY=\S+\b(.*)/ $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 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  SMTP  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 2.2 and later.

smtpd_discard_ehlo_keywords (default: empty)
       A  case  insensitive list of EHLO keywords (pipelining, starttls, auth,
       etc.) that the 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_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 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 off by default and should be used only on dedicated servers.

       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  SMTP  server  access  restrictions in the context of a client
       ETRN request.  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  the  SMTP  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_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 syntax is
              invalid. 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 send-
              ing 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 form, as required by the RFC. Note: spec-
              ify "smtpd_helo_required = yes" to fully enforce  this  restric-
              tion  (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  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..number 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
              configuration 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 sending 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 unknown_hostname_reject_code parameter specifies the numeri-
              cal response code for rejected requests (default: 450).
              The  unknown_helo_hostname_tempfail_action  parameter  specifies
              the  action  after a temporary DNS error (default: defer_if_per-
              mit). 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_milters (default: empty)
       A list of Milter (mail filter) applications for new mail  that  arrives
       via  the  Postfix  smtpd(8) server.  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_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_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_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 accepting 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: permit_mynetworks, reject_unauth_desti-
       nation)
       The  access  restrictions  that  the Postfix SMTP server applies in the
       context of the  RCPT  TO  command.   See  SMTPD_ACCESS_README,  section
       "Delayed  evaluation of SMTP access restriction lists" for a discussion
       of evaluation context and time.

       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: If you change this parameter setting, you  must  specify  at
       least  one of the following restrictions. Otherwise Postfix will refuse
       to receive mail:

           reject, defer, defer_if_permit, reject_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_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).

       reject_unknown_recipient_domain
              Reject the request when Postfix is not final destination for the
              recipient domain, and the RCPT TO domain has  no  DNS  A  or  MX
              record,  or  when  it has a malformed MX record such as a record
              with a zero-length MX hostname (Postfix version 2.3 and  later).
              The  unknown_address_reject_code parameter specifies the numeri-
              cal response code for rejected  requests  (default:  450).   The
              response is always 450 in case of a temporary DNS error.
              The   unknown_address_tempfail_action  parameter  specifies  the
              action after a temporary DNS error (default: defer_if_permit).

       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  addres  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:

       smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination

smtpd_reject_footer (default: empty)
       Optional information that is appended after each SMTP server 4XX or 5XX
       response.

       Example:

       /etc/postfix/main.cf:
           smtpd_reject_footer = 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
           550 5.5.1 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.

       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_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:

           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_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  sender  (MAIL
       FROM) addresses.

       Specify  zero  or  more  "type:table"  lookup tables. With lookups from
       indexed files such as DB or DBM, or from networked tables such as  NIS,
       LDAP  or  SQL,  the  following search operations 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  the  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_mx_access type:table
              Search the specified access(5) database for the MX hosts for the
              MAIL FROM address, 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 address, 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_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 address has no  DNS  A  or  MX
              record,  or  when  it has a malformed MX record such as a record
              with a zero-length MX hostname (Postfix version 2.3 and  later).
              The  unknown_address_reject_code parameter specifies the numeri-
              cal response code for rejected  requests  (default:  450).   The
              response is always 450 in case of a temporary DNS error.
              The   unknown_address_tempfail_action  parameter  specifies  the
              action after a temporary DNS error (default: defer_if_permit).

       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 address probe failed due to a tem-
              porary 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)  forwards  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 "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  certifi-
       cate 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 certificate authori-
       ties 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  "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   certificate   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 certificate authorities to select the correct client certifi-
       cate.    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
       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  simi-
       lar 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 inter-operability 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: export)
       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  "export"  ensures  maximum
       inter-operability.  Because  encryption  is optional, stronger controls
       are not appropriate, and this setting SHOULD NOT be changed unless  the
       change is essential.

       When   TLS   is   mandatory   the   cipher  grade  is  chosen  via  the
       smtpd_tls_mandatory_ciphers configuration parameter, see there for syn-
       tax details.

       Example:
       smtpd_tls_ciphers = export

       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
       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 command:

           openssl gendh -out /etc/postfix/dh_1024.pem -2 1024

       Your actual source for entropy may differ. Some systems have  /dev/ran-
       dom; on other system you may consider using the "Entropy Gathering Dae-
       mon EGD", available at http://egd.sourceforge.net/

       Example:

       smtpd_tls_dh1024_param_file = /etc/postfix/dh_1024.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
       EDH ciphers.

       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.

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

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 used to construct client-certificate  fin-
       gerprints   for   check_ccert_access  and  permit_tls_clientcerts.  The
       default algorithm is md5,  for  backwards  compatibility  with  Postfix
       releases prior to 2.5.

       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

       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 TLS handshake and certificate information.

              2 Log levels during TLS negotiation.

              3 Log hexadecimal and ASCII dump of TLS negotiation process.

              4 Also log hexadecimal and ASCII dump of  complete  transmission
              after STARTTLS.

       Use  "smtpd_tls_loglevel = 3" only in case of problems. 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.  This is  the
              most appropriate setting for public MX hosts, and is always used
              with opportunistic TLS encryption. The underlying cipherlist  is
              specified via the tls_export_cipherlist configuration parameter,
              which you are strongly encouraged to not change.

       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.

       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 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  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)
       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 supported
       protocol  names are "SSLv2", "SSLv3" and "TLSv1", and are not case sen-
       sitive.

       Note: As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1"  and
       "TLSv1.2".  If an older Postfix version is linked against OpenSSL 1.0.1
       or later, these, or any other new protocol versions,  are  uncondition-
       ally enabled.

       With  Postfix >= 2.5 the parameter syntax is expanded to support proto-
       col exclusions.  One  can  now  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 supported,
       but not recommended. The exclusion form more closely matches the behav-
       iour when the OpenSSL library is newer than Postfix.

       Since  SSL  version  2  has known protocol weaknesses and is now depre-
       cated, the default  setting  excludes  "SSLv2".   This  means  that  by
       default,  SSL  version  2  will  not  be used at the "encrypt" security
       level.

       Example:

       smtpd_tls_mandatory_protocols = TLSv1
       # Alternative form with Postfix >= 2.5:
       smtpd_tls_mandatory_protocols = !SSLv2, !SSLv3

       This feature is available in Postfix 2.3 and later.

smtpd_tls_protocols (default: empty)
       List of TLS protocols that the Postfix  SMTP  server  will  exclude  or
       include  with  opportunistic  TLS  encryption. This parameter SHOULD be
       left at its default empty value, allowing all protocols to be used with
       opportunistic TLS.

       In main.cf the values are separated by whitespace, commas or colons. An
       empty value means allow all protocols. The valid protocol  names,  (see
       \fBfBSSL_get_version(3)),   are   "SSLv2",   "SSLv3"  and  "TLSv1".  In
       smtp_tls_policy_maps table entries, "protocols"  attribute  values  are
       separated by a colon.

       Note:  As of OpenSSL 1.0.1 two new protocols are defined, "TLSv1.1" and
       "TLSv1.2". If an older Postfix version is linked against OpenSSL  1.0.1
       or  later,  these, or any other new protocol versions, are uncondition-
       ally enabled.

       To include a protocol list its name, to exclude  it,  prefix  the  name
       with  a  "!" character. To exclude SSLv2 even 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 behaviour
       when the OpenSSL library is newer than Postfix.

       Example:
       smtpd_tls_protocols = !SSLv2

       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 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 SMTP clients,
              but do not require that clients use TLS encryption.

       encrypt
              Mandatory TLS encryption:  announce  STARTTLS  support  to  SMTP
              clients,  and require that clients use TLS encryption. According
              to RFC 2487 this MUST NOT be applied in case of a  publicly-ref-
              erenced 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 SMTP client certificates, see TLS_README for a dis-
       cussion  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.

       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.

       This feature is available in Postfix 2.2 and later.

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_use_tls (default: no)
       Opportunistic TLS: announce STARTTLS support to 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.

soft_bounce (default: no)
       Safety net to keep mail queued that would otherwise be returned to  the
       sender.   This  parameter  disables locally-generated bounces, and pre-
       vents the Postfix SMTP  server  from  rejecting  mail  permanently,  by
       changing 5xx reply codes into 4xx.  However, soft_bounce is no cure for
       address rewriting mistakes or mail routing mistakes.

       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.

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 certificate  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_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  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.

       This default curve is specified in  NSA  "Suite  B"  Cryptography  (see
       http://www.nsa.gov/ia/industry/crypto_suite_b.cfm)    for   information
       classified as 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.

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

tls_eecdh_ultra_curve (default: secp384r1)
       The elliptic curve  used  by  the  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 specified in NSA "Suite B" Cryptography
       (see http://www.nsa.gov/ia/industry/crypto_suite_b.cfm) for information
       classified as TOP SECRET.

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

tls_export_cipherlist (default: ALL:+RC4:@STRENGTH)
       The OpenSSL cipherlist for  "EXPORT"  or  higher  grade  ciphers.  This
       defines  the  meaning  of  the  "export"  setting  in  smtpd_tls_manda-
       tory_ciphers,    smtp_tls_mandatory_ciphers     and     lmtp_tls_manda-
       tory_ciphers.  This is the cipherlist for the opportunistic ("may") TLS
       client security level and  is  the  default  cipherlist  for  the  SMTP
       server.  You  are  strongly encouraged to not change this setting. With
       OpenSSL 1.0.0 and later the cipherlist may start with an "aNULL:"  pre-
       fix,  which restores the 0.9.8-compatible ordering of the aNULL ciphers
       to the top of the list when they are enabled. This prefix is not needed
       with previous OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_high_cipherlist (default: ALL:!EXPORT:!LOW:!MEDIUM:+RC4:@STRENGTH)
       The OpenSSL cipherlist for "HIGH" grade ciphers. This defines the mean-
       ing   of   the   "high"   setting    in    smtpd_tls_mandatory_ciphers,
       smtp_tls_mandatory_ciphers   and  lmtp_tls_mandatory_ciphers.  You  are
       strongly encouraged to not change this setting. With OpenSSL 1.0.0  and
       later  the cipherlist may start with an "aNULL:" prefix, which restores
       the 0.9.8-compatible ordering of the aNULL ciphers to the  top  of  the
       list  when  they  are  enabled. This prefix is not needed with previous
       OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_low_cipherlist (default: ALL:!EXPORT:+RC4:@STRENGTH)
       The OpenSSL cipherlist for "LOW" or higher grade ciphers. This  defines
       the  meaning  of  the  "low"  setting  in  smtpd_tls_mandatory_ciphers,
       smtp_tls_mandatory_ciphers  and  lmtp_tls_mandatory_ciphers.  You   are
       strongly encouraged to not change this setting.  With OpenSSL 1.0.0 and
       later the cipherlist may start with an "aNULL:" prefix, which  restores
       the  0.9.8-compatible  ordering  of the aNULL ciphers to the top of the
       list when they are enabled. This prefix is  not  needed  with  previous
       OpenSSL releases.

       This feature is available in Postfix 2.3 and later.

tls_medium_cipherlist (default: ALL:!EXPORT:!LOW:+RC4:@STRENGTH)
       The  OpenSSL  cipherlist  for  "MEDIUM"  or  higher grade ciphers. This
       defines  the  meaning  of  the  "medium"  setting  in  smtpd_tls_manda-
       tory_ciphers,     smtp_tls_mandatory_ciphers     and    lmtp_tls_manda-
       tory_ciphers. This is the default cipherlist for mandatory TLS  encryp-
       tion  in the TLS client (with anonymous ciphers disabled when verifying
       server certificates). You are strongly encouraged to  not  change  this
       setting.  With OpenSSL 1.0.0 and later the cipherlist may start with an
       "aNULL:" prefix, which restores the 0.9.8-compatible  ordering  of  the
       aNULL ciphers to the top of the list when they are enabled. This prefix
       is not needed with previous OpenSSL releases.

       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 server's cipher preference order  instead
       of the 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.

       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.

tlsproxy_enforce_tls (default: $smtpd_enforce_tls)
       Mandatory  TLS:  announce STARTTLS support to SMTP clients, and require
       that clients use TLS  encryption.  See  smtpd_enforce_tls  for  further
       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  EDH ciphers. See smtpd_tls_dh1024_param_file for further 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 EDH ciphers. See smtpd_tls_dh512_param_file for further details.

       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 elliptic-
       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 used to construct client-certificate fin-
       gerprints. 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)

       The  expiration  time  of  Postfix tlsproxy(8) server TLS session cache
       information.  A  cache  cleanup   is   performed   periodically   every
       $smtpd_tls_session_cache_timeout     seconds.     See    smtpd_tls_ses-
       sion_cache_timeout for further details.

       This feature is available in Postfix 2.8 and later.

tlsproxy_use_tls (default: $smtpd_use_tls)
       Opportunistic TLS: announce STARTTLS support to SMTP  clients,  but  do
       not require that clients use TLS encryption. See smtpd_use_tls for fur-
       ther 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  (seconds),
       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.

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.

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.

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.

       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.

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.

       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.

       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.

       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.

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.

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.

       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.  If you use this  fea-
       ture  with local files, run "postmap /etc/postfix/transport" after mak-
       ing a change.

       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.

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.

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.

       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.

       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.

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 Postfix SMTP server response code when a sender or recip-
       ient  address  is  rejected  by  the  reject_unknown_sender_domain   or
       reject_unknown_recipient_domain  restriction.   The  response is always
       450 in case of a temporary DNS error.

       Do not change this unless you have  a  complete  understanding  of  RFC
       2821.

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
       2821.

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
       2821.

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  SMTP  server  reply  code  when  a recipient address matches $vir-
       tual_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  SMTP  server  reply  code  when  a recipient address matches $vir-
       tual_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
       2821.

       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
       2821.

       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
       2821.

       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
       2821.

       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_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.

       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_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.

       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.

       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).

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  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.

       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 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.

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.

       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



                                                                   POSTCONF(5)

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