oqmgr - old Postfix queue manager
oqmgr [generic Postfix daemon options]
The oqmgr(8) daemon awaits the arrival of incoming mail and arranges for its delivery via Postfix delivery processes. The actual mail rout- ing strategy is delegated to the trivial-rewrite(8) daemon. This pro- gram expects to be run from the master(8) process manager. Mail addressed to the local double-bounce address is logged and dis- carded. This stops potential loops caused by undeliverable bounce notifications.
The oqmgr(8) daemon maintains the following queues: incoming Inbound mail from the network, or mail picked up by the local pickup(8) agent from the maildrop directory. active Messages that the queue manager has opened for delivery. Only a limited number of messages is allowed to enter the active queue (leaky bucket strategy, for a fixed delivery rate). deferred Mail that could not be delivered upon the first attempt. The queue manager implements exponential backoff by doubling the time between delivery attempts. corrupt Unreadable or damaged queue files are moved here for inspection. hold Messages that are kept "on hold" are kept here until someone sets them free.
DELIVERY STATUS REPORTS
The oqmgr(8) daemon keeps an eye on per-message delivery status reports in the following directories. Each status report file has the same name as the corresponding message file: bounce Per-recipient status information about why mail is bounced. These files are maintained by the bounce(8) daemon. defer Per-recipient status information about why mail is delayed. These files are maintained by the defer(8) daemon. trace Per-recipient status information as requested with the Postfix "sendmail -v" or "sendmail -bv" command. These files are main- tained by the trace(8) daemon. The oqmgr(8) daemon is responsible for asking the bounce(8), defer(8) or trace(8) daemons to send delivery reports.
The queue manager implements a variety of strategies for either opening queue files (input) or for message delivery (output). leaky bucket This strategy limits the number of messages in the active queue and prevents the queue manager from running out of memory under heavy load. fairness When the active queue has room, the queue manager takes one mes- sage from the incoming queue and one from the deferred queue. This prevents a large mail backlog from blocking the delivery of new mail. slow start This strategy eliminates "thundering herd" problems by slowly adjusting the number of parallel deliveries to the same destina- tion. round robin The queue manager sorts delivery requests by destination. Round-robin selection prevents one destination from dominating deliveries to other destinations. exponential backoff Mail that cannot be delivered upon the first attempt is deferred. The time interval between delivery attempts is dou- bled after each attempt. destination status cache The queue manager avoids unnecessary delivery attempts by main- taining a short-term, in-memory list of unreachable destina- tions.
On an idle system, the queue manager waits for the arrival of trigger events, or it waits for a timer to go off. A trigger is a one-byte mes- sage. Depending on the message received, the queue manager performs one of the following actions (the message is followed by the symbolic constant used internally by the software): D (QMGR_REQ_SCAN_DEFERRED) Start a deferred queue scan. If a deferred queue scan is already in progress, that scan will be restarted as soon as it finishes. I (QMGR_REQ_SCAN_INCOMING) Start an incoming queue scan. If an incoming queue scan is already in progress, that scan will be restarted as soon as it finishes. A (QMGR_REQ_SCAN_ALL) Ignore deferred queue file time stamps. The request affects the next deferred queue scan. F (QMGR_REQ_FLUSH_DEAD) Purge all information about dead transports and destinations. W (TRIGGER_REQ_WAKEUP) Wakeup call, This is used by the master server to instantiate servers that should not go away forever. The action is to start an incoming queue scan. The oqmgr(8) daemon reads an entire buffer worth of triggers. Multiple identical trigger requests are collapsed into one, and trigger requests are sorted so that A and F precede D and I. Thus, in order to force a deferred queue run, one would request A F D; in order to notify the queue manager of the arrival of new mail one would request I.
RFC 3463 (Enhanced status codes) RFC 3464 (Delivery status notifications)
The oqmgr(8) daemon is not security sensitive. It reads single-charac- ter messages from untrusted local users, and thus may be susceptible to denial of service attacks. The oqmgr(8) daemon does not talk to the outside world, and it can be run at fixed low privilege in a chrooted environment.
Problems and transactions are logged to the syslog(8) daemon. Cor- rupted message files are saved to the corrupt queue for further inspec- tion. Depending on the setting of the notify_classes parameter, the postmas- ter is notified of bounces and of other trouble.
A single queue manager process has to compete for disk access with mul- tiple front-end processes such as cleanup(8). A sudden burst of inbound mail can negatively impact outbound delivery rates.
Changes to main.cf are not picked up automatically, as oqmgr(8) is a persistent process. Use the command "postfix reload" after a configura- tion change. The text below provides only a parameter summary. See postconf(5) for more details including examples. In the text below, transport is the first field in a master.cf entry.
Available before Postfix version 2.5: allow_min_user (no) Allow a sender or recipient address to have `-' as the first character.
ACTIVE QUEUE CONTROLS
qmgr_clog_warn_time (300s) The minimal delay between warnings that a specific destination is clogging up the Postfix active queue. qmgr_message_active_limit (20000) The maximal number of messages in the active queue. qmgr_message_recipient_limit (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.
DELIVERY CONCURRENCY CONTROLS
qmgr_fudge_factor (100) Obsolete feature: the percentage of delivery resources that a busy mail system will use up for delivery of a large mailing list message. initial_destination_concurrency (5) The initial per-destination concurrency level for parallel delivery to the same destination. default_destination_concurrency_limit (20) The default maximal number of parallel deliveries to the same destination. transport_destination_concurrency_limit ($default_destination_concur- rency_limit) Idem, for delivery via the named message transport. Available in Postfix version 2.5 and later: transport_initial_destination_concurrency ($initial_destination_concur- rency) Initial concurrency for delivery via the named message trans- port. default_destination_concurrency_failed_cohort_limit (1) How many pseudo-cohorts must suffer connection or handshake failure before a specific destination is considered unavailable (and further delivery is suspended). transport_destination_concurrency_failed_cohort_limit ($default_desti- nation_concurrency_failed_cohort_limit) Idem, for delivery via the named message transport. default_destination_concurrency_negative_feedback (1) The per-destination amount of delivery concurrency negative feedback, after a delivery completes with a connection or hand- shake failure. transport_destination_concurrency_negative_feedback ($default_destina- tion_concurrency_negative_feedback) Idem, for delivery via the named message transport. default_destination_concurrency_positive_feedback (1) The per-destination amount of delivery concurrency positive feedback, after a delivery completes without connection or hand- shake failure. transport_destination_concurrency_positive_feedback ($default_destina- tion_concurrency_positive_feedback) Idem, for delivery via the named message transport. destination_concurrency_feedback_debug (no) Make the queue manager's feedback algorithm verbose for perfor- mance analysis purposes.
RECIPIENT SCHEDULING CONTROLS
default_destination_recipient_limit (50) The default maximal number of recipients per message delivery. transport_destination_recipient_limit Idem, for delivery via the named message transport.
OTHER RESOURCE AND RATE CONTROLS
minimal_backoff_time (300s) The minimal time between attempts to deliver a deferred message; prior to Postfix 2.4 the default value was 1000s. maximal_backoff_time (4000s) The maximal time between attempts to deliver a deferred message. maximal_queue_lifetime (5d) The maximal time a message is queued before it is sent back as undeliverable. queue_run_delay (300s) The time between deferred queue scans by the queue manager; prior to Postfix 2.4 the default value was 1000s. transport_retry_time (60s) The time between attempts by the Postfix queue manager to con- tact a malfunctioning message delivery transport. Available in Postfix version 2.1 and later: bounce_queue_lifetime (5d) The maximal time a bounce message is queued before it is consid- ered undeliverable. Available in Postfix version 2.5 and later: default_destination_rate_delay (0s) The default amount of delay that is inserted between individual deliveries to the same destination; with per-destination recipi- ent limit > 1, a destination is a domain, otherwise it is a recipient. transport_destination_rate_delay $default_destination_rate_delay Idem, for delivery via the named message transport.
config_directory (see 'postconf -d' output) The default location of the Postfix main.cf and master.cf con- figuration files. daemon_timeout (18000s) How much time a Postfix daemon process may take to handle a request before it is terminated by a built-in watchdog timer. defer_transports (empty) The names of message delivery transports that should not deliver mail unless someone issues "sendmail -q" or equivalent. delay_logging_resolution_limit (2) The maximal number of digits after the decimal point when log- ging sub-second delay values. helpful_warnings (yes) Log warnings about problematic configuration settings, and pro- vide helpful suggestions. ipc_timeout (3600s) The time limit for sending or receiving information over an internal communication channel. process_id (read-only) The process ID of a Postfix command or daemon process. process_name (read-only) The process name of a Postfix command or daemon process. queue_directory (see 'postconf -d' output) The location of the Postfix top-level queue directory. syslog_facility (mail) The syslog facility of Postfix logging. syslog_name (postfix) The mail system name that is prepended to the process name in syslog records, so that "smtpd" becomes, for example, "post- fix/smtpd".
/var/spool/postfix/incoming, incoming queue /var/spool/postfix/active, active queue /var/spool/postfix/deferred, deferred queue /var/spool/postfix/bounce, non-delivery status /var/spool/postfix/defer, non-delivery status /var/spool/postfix/trace, delivery status
trivial-rewrite(8), address routing bounce(8), delivery status reports postconf(5), configuration parameters master(5), generic daemon options master(8), process manager syslogd(8), system logging
Use "postconf readme_directory" or "postconf html_directory" to locate this information. QSHAPE_README, Postfix queue analysis
The Secure Mailer license must be distributed with this software.
Wietse Venema IBM T.J. Watson Research P.O. Box 704 Yorktown Heights, NY 10598, USA OQMGR(8)
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