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QMGR(8) System Manager's Manual QMGR(8) NAME qmgr - Postfix queue manager SYNOPSIS qmgr [generic Postfix daemon options] DESCRIPTION The qmgr(8) daemon awaits the arrival of incoming mail and arranges for its delivery via Postfix delivery processes. The actual mail routing strategy is delegated to the trivial-rewrite(8) daemon. This program 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 no- tifications. MAIL QUEUES The qmgr(8) daemon maintains the following queues: incoming Inbound mail from the network, or mail picked up by the local pickup(8) daemon 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 qmgr(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 qmgr(8) daemon is responsible for asking the bounce(8), defer(8) or trace(8) daemons to send delivery reports. STRATEGIES 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 de- ferred. The time interval between delivery attempts is doubled 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. preemptive message scheduling The queue manager attempts to minimize the average per-recipient delay while still preserving the correct per-message delays, us- ing a sophisticated preemptive message scheduling. TRIGGERS 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 al- ready 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 al- ready 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 qmgr(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. STANDARDS RFC 3463 (Enhanced status codes) RFC 3464 (Delivery status notifications) SECURITY The qmgr(8) daemon is not security sensitive. It reads single-character messages from untrusted local users, and thus may be susceptible to de- nial of service attacks. The qmgr(8) daemon does not talk to the out- side world, and it can be run at fixed low privilege in a chrooted en- vironment. DIAGNOSTICS Problems and transactions are logged to syslogd(8) or postlogd(8). Corrupted message files are saved to the corrupt queue for further in- spection. Depending on the setting of the notify_classes parameter, the postmas- ter is notified of bounces and of other trouble. BUGS 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. CONFIGURATION PARAMETERS Changes to main.cf are not picked up automatically as qmgr(8) is a per- sistent process. Use the "postfix reload" command after a configuration 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. COMPATIBILITY CONTROLS Available before Postfix version 2.5: allow_min_user (no) Allow a sender or recipient address to have `-' as the first character. Available with Postfix version 2.7 and later: default_filter_nexthop (empty) When a content_filter or FILTER request specifies no explicit next-hop destination, use $default_filter_nexthop instead; when that value is empty, use the domain in the recipient address. ACTIVE QUEUE CONTROLS qmgr_clog_warn_time (300s) The minimal delay between warnings that a specific destination is clogging up the Postfix active queue. qmgr_message_active_limit (20000) The maximal number of messages in the active queue. qmgr_message_recipient_limit (20000) The maximal number of recipients held in memory by the Postfix queue manager, and the maximal size of the short-term, in-memory "dead" destination status cache. qmgr_message_recipient_minimum (10) The minimal number of in-memory recipients for any message. default_recipient_limit (20000) The default per-transport upper limit on the number of in-memory recipients. transport_recipient_limit ($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. default_extra_recipient_limit (1000) The default value for the extra per-transport limit imposed on the number of in-memory recipients. transport_extra_recipient_limit ($default_extra_recipient_limit) A transport-specific override for the default_extra_recipi- ent_limit parameter value, where transport is the master.cf name of the message delivery transport. Available in Postfix version 2.4 and later: default_recipient_refill_limit (100) The default per-transport limit on the number of recipients re- filled at once. transport_recipient_refill_limit ($default_recipient_refill_limit) A transport-specific override for the default_recipient_re- fill_limit parameter value, where transport is the master.cf name of the message delivery transport. default_recipient_refill_delay (5s) The default per-transport maximum delay between refilling recip- ients. transport_recipient_refill_delay ($default_recipient_refill_delay) A transport-specific override for the default_recipient_re- fill_delay parameter value, where transport is the master.cf name of the message delivery transport. DELIVERY CONCURRENCY CONTROLS initial_destination_concurrency (5) The initial per-destination concurrency level for parallel de- livery to the same destination. default_destination_concurrency_limit (20) The default maximal number of parallel deliveries to the same destination. transport_destination_concurrency_limit ($default_destination_concur- rency_limit) A transport-specific override for the default_destination_con- currency_limit parameter value, where transport is the master.cf name of the message delivery transport. Available in Postfix version 2.5 and later: transport_initial_destination_concurrency ($initial_destination_concur- rency) A transport-specific override for the initial_destination_con- currency parameter value, where transport is the master.cf name of the message delivery transport. default_destination_concurrency_failed_cohort_limit (1) How many pseudo-cohorts must suffer connection or handshake failure before a specific destination is considered unavailable (and further delivery is suspended). transport_destination_concurrency_failed_cohort_limit ($default_desti- nation_concurrency_failed_cohort_limit) A transport-specific override for the default_destination_con- currency_failed_cohort_limit parameter value, where transport is the master.cf name of the message delivery 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 ($default_destina- tion_concurrency_negative_feedback) A transport-specific override for the default_destination_con- currency_negative_feedback parameter value, where transport is the master.cf name of the message delivery transport. default_destination_concurrency_positive_feedback (1) The per-destination amount of delivery concurrency positive feedback, after a delivery completes without connection or hand- shake failure. transport_destination_concurrency_positive_feedback ($default_destina- tion_concurrency_positive_feedback) A transport-specific override for the default_destination_con- currency_positive_feedback parameter value, where transport is the master.cf name of the message delivery 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 ($default_destination_recipi- ent_limit) A transport-specific override for the default_destination_recip- ient_limit parameter value, where transport is the master.cf name of the message delivery transport. MESSAGE SCHEDULING CONTROLS default_delivery_slot_cost (5) How often the Postfix queue manager's scheduler is allowed to preempt delivery of one message with another. transport_delivery_slot_cost ($default_delivery_slot_cost) A transport-specific override for the default_delivery_slot_cost parameter value, where transport is the master.cf name of the message delivery transport. default_minimum_delivery_slots (3) How many recipients a message must have in order to invoke the Postfix queue manager's scheduling algorithm at all. transport_minimum_delivery_slots ($default_minimum_delivery_slots) A transport-specific override for the default_minimum_deliv- ery_slots parameter value, where transport is the master.cf name of the message delivery transport. default_delivery_slot_discount (50) The default value for transport-specific _delivery_slot_discount settings. transport_delivery_slot_discount ($default_delivery_slot_discount) A transport-specific override for the default_delivery_slot_dis- count parameter value, where transport is the master.cf name of the message delivery transport. default_delivery_slot_loan (3) The default value for transport-specific _delivery_slot_loan settings. transport_delivery_slot_loan ($default_delivery_slot_loan) A transport-specific override for the default_delivery_slot_loan parameter value, where transport is the master.cf name of the message delivery transport. OTHER RESOURCE AND RATE CONTROLS minimal_backoff_time (300s) The minimal time between attempts to deliver a deferred message; prior to Postfix 2.4 the default value was 1000s. maximal_backoff_time (4000s) The maximal time between attempts to deliver a deferred message. maximal_queue_lifetime (5d) Consider a message as undeliverable, when delivery fails with a temporary error, and the time in the queue has reached the maxi- mal_queue_lifetime limit. queue_run_delay (300s) The time between deferred queue scans by the queue manager; prior to Postfix 2.4 the default value was 1000s. transport_retry_time (60s) The time between attempts by the Postfix queue manager to con- tact a malfunctioning message delivery transport. Available in Postfix version 2.1 and later: bounce_queue_lifetime (5d) Consider a bounce message as undeliverable, when delivery fails with a temporary error, and the time in the queue has reached the bounce_queue_lifetime limit. Available in Postfix version 2.5 and later: default_destination_rate_delay (0s) The default amount of delay that is inserted between individual message deliveries to the same destination and over the same message delivery transport. transport_destination_rate_delay ($default_destination_rate_delay) A transport-specific override for the default_destina- tion_rate_delay parameter value, where transport is the mas- ter.cf name of the message delivery transport. Available in Postfix version 3.1 and later: default_transport_rate_delay (0s) The default amount of delay that is inserted between individual message deliveries over the same message delivery transport, re- gardless of destination. transport_transport_rate_delay ($default_transport_rate_delay) A transport-specific override for the default_transport_rate_de- lay parameter value, where the initial transport in the parame- ter name is the master.cf name of the message delivery trans- port. SAFETY CONTROLS qmgr_daemon_timeout (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. qmgr_ipc_timeout (60s) The time limit for the queue manager to send or receive informa- tion over an internal communication channel. Available in Postfix version 3.1 and later: address_verify_pending_request_limit (see 'postconf -d' output) A safety limit that prevents address verification requests from overwhelming the Postfix queue. MISCELLANEOUS CONTROLS config_directory (see 'postconf -d' output) The default location of the Postfix main.cf and master.cf con- figuration files. 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. 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 (see 'postconf -d' output) A prefix that is prepended to the process name in syslog records, so that, for example, "smtpd" becomes "prefix/smtpd". Available in Postfix version 3.0 and later: confirm_delay_cleared (no) After sending a "your message is delayed" notification, inform the sender when the delay clears up. Available in Postfix 3.3 and later: service_name (read-only) The master.cf service name of a Postfix daemon process. Available in Postfix 3.5 and later: info_log_address_format (external) The email address form that will be used in non-debug logging (info, warning, etc.). FILES /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 SEE ALSO trivial-rewrite(8), address routing bounce(8), delivery status reports postconf(5), configuration parameters master(5), generic daemon options master(8), process manager postlogd(8), Postfix logging syslogd(8), system logging README FILES Use "postconf readme_directory" or "postconf html_directory" to locate this information. SCHEDULER_README, scheduling algorithm QSHAPE_README, Postfix queue analysis 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 Preemptive scheduler enhancements: Patrik Rak Modra 6 155 00, Prague, Czech Republic Wietse Venema Google, Inc. 111 8th Avenue New York, NY 10011, USA QMGR(8)
NAME | SYNOPSIS | DESCRIPTION | MAIL QUEUES | DELIVERY STATUS REPORTS | STRATEGIES | TRIGGERS | STANDARDS | SECURITY | DIAGNOSTICS | BUGS | CONFIGURATION PARAMETERS | COMPATIBILITY CONTROLS | ACTIVE QUEUE CONTROLS | DELIVERY CONCURRENCY CONTROLS | RECIPIENT SCHEDULING CONTROLS | MESSAGE SCHEDULING CONTROLS | OTHER RESOURCE AND RATE CONTROLS | SAFETY CONTROLS | MISCELLANEOUS CONTROLS | FILES | SEE ALSO | README FILES | LICENSE | AUTHOR(S)
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