# man > qmgr(8) [_QMGR_(8postfix)](https://www.chedong.com/phpMan.php/man/QMGR/8postfix/markdown) [_QMGR_(8postfix)](https://www.chedong.com/phpMan.php/man/QMGR/8postfix/markdown) ## NAME qmgr - Postfix queue manager ## SYNOPSIS **qmgr **[generic Postfix daemon options] ## DESCRIPTION The [**qmgr**(8)](https://www.chedong.com/phpMan.php/man/qmgr/8/markdown) 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 **triv‐** [**ial-rewrite**(8)](https://www.chedong.com/phpMan.php/man/ial-rewrite/8/markdown) daemon. This program expects to be run from the [**master**(8)](https://www.chedong.com/phpMan.php/man/master/8/markdown) process manager. Mail addressed to the local **double-bounce **address is logged and discarded. This stops poten‐ tial loops caused by undeliverable bounce notifications. ## MAIL QUEUES The [**qmgr**(8)](https://www.chedong.com/phpMan.php/man/qmgr/8/markdown) daemon maintains the following queues: ### incoming Inbound mail from the network, or mail picked up by the local [**pickup**(8)](https://www.chedong.com/phpMan.php/man/pickup/8/markdown) daemon from the **maildrop **directory. **active **Messages that the queue manager has opened for delivery. Only a limited number of mes‐ sages is allowed to enter the **active **queue (leaky bucket strategy, for a fixed deliv‐ ery 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)](https://www.chedong.com/phpMan.php/man/qmgr/8/markdown) daemon keeps an eye on per-message delivery status reports in the following di‐ rectories. 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 main‐ tained by the [**bounce**(8)](https://www.chedong.com/phpMan.php/man/bounce/8/markdown) daemon. **defer **Per-recipient status information about why mail is delayed. These files are main‐ tained by the [**defer**(8)](https://www.chedong.com/phpMan.php/man/defer/8/markdown) daemon. **trace **Per-recipient status information as requested with the Postfix "**sendmail -v**" or "**send‐** **mail -bv**" command. These files are maintained by the [**trace**(8)](https://www.chedong.com/phpMan.php/man/trace/8/markdown) daemon. The [**qmgr**(8)](https://www.chedong.com/phpMan.php/man/qmgr/8/markdown) daemon is responsible for asking the [**bounce**(8)](https://www.chedong.com/phpMan.php/man/bounce/8/markdown), [**defer**(8)](https://www.chedong.com/phpMan.php/man/defer/8/markdown) or [**trace**(8)](https://www.chedong.com/phpMan.php/man/trace/8/markdown) 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 message from the **incoming** queue and one from the **deferred **queue. This prevents a large mail backlog from block‐ ing the delivery of new mail. ### slow start This strategy eliminates "thundering herd" problems by slowly adjusting the number of parallel deliveries to the same destination. ### round robin The queue manager sorts delivery requests by destination. Round-robin selection pre‐ vents 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 doubled after each attempt. ### destination status cache The queue manager avoids unnecessary delivery attempts by maintaining a short-term, in-memory list of unreachable destinations. ### preemptive message scheduling The queue manager attempts to minimize the average per-recipient delay while still preserving the correct per-message delays, using 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 message. 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 [**qmgr**(8)](https://www.chedong.com/phpMan.php/man/qmgr/8/markdown) daemon reads an entire buffer worth of triggers. Multiple identical trigger re‐ quests 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)](https://www.chedong.com/phpMan.php/man/qmgr/8/markdown) daemon is not security sensitive. It reads single-character messages from un‐ trusted local users, and thus may be susceptible to denial of service attacks. The [**qmgr**(8)](https://www.chedong.com/phpMan.php/man/qmgr/8/markdown) daemon does not talk to the outside world, and it can be run at fixed low privilege in a ch‐ rooted environment. ## DIAGNOSTICS Problems and transactions are logged to [**syslogd**(8)](https://www.chedong.com/phpMan.php/man/syslogd/8/markdown) or [**postlogd**(8)](https://www.chedong.com/phpMan.php/man/postlogd/8/markdown). Corrupted message files are saved to the **corrupt **queue for further inspection. Depending on the setting of the **notify_classes **parameter, the postmaster is notified of bounces and of other trouble. ## BUGS A single queue manager process has to compete for disk access with multiple front-end processes such as [**cleanup**(8)](https://www.chedong.com/phpMan.php/man/cleanup/8/markdown). 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)](https://www.chedong.com/phpMan.php/man/qmgr/8/markdown) is a persistent process. Use the "**postfix reload**" command after a configuration change. The text below provides only a parameter summary. See [**postconf**(5)](https://www.chedong.com/phpMan.php/man/postconf/5/markdown) 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 ($default_extra_recipient_limit) A transport-specific override for the default_extra_recipient_limit parameter value, where _transport_ is the master.cf name of the message delivery transport. Available in Postfix version 2.4 and later: ### default_recipient_refill_limit (100) The default per-transport limit on the number of recipients refilled at once. ### transport_recipient_refill_limit ($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. ### default_recipient_refill_delay (5s) The default per-transport maximum delay between recipients refills. ### transport_recipient_refill_delay ($default_recipient_refill_delay) A transport-specific override for the default_recipient_refill_delay parameter value, where _transport_ is the master.cf name of the message delivery transport. ## DELIVERY CONCURRENCY CONTROLS ### initial_destination_concurrency (5) The initial per-destination concurrency level for parallel delivery to the same desti‐ nation. ### default_destination_concurrency_limit (20) The default maximal number of parallel deliveries to the same destination. ### transport_destination_concurrency_limit ($default_destination_concurrency_limit) A transport-specific override for the default_destination_concurrency_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 ($initial_destination_concurrency) A transport-specific override for the initial_destination_concurrency parameter value, where _transport_ is the master.cf name of the message delivery transport. ### default_destination_concurrency_failed_cohort_limit (1) How many pseudo-cohorts must suffer connection or handshake failure before a specific destination is considered unavailable (and further delivery is suspended). ### transport_destination_concurrency_failed_cohort_limit ($default_destination_concur‐ ### rency_failed_cohort_limit) A transport-specific override for the default_destination_concurrency_failed_co‐ hort_limit parameter value, where _transport_ is the master.cf name of the message de‐ livery transport. ### default_destination_concurrency_negative_feedback (1) The per-destination amount of delivery concurrency negative feedback, after a delivery completes with a connection or handshake failure. ### transport_destination_concurrency_negative_feedback ($default_destination_concurrency_nega‐ ### tive_feedback) A transport-specific override for the default_destination_concurrency_negative_feed‐ back parameter value, where _transport_ is the master.cf name of the message delivery transport. ### default_destination_concurrency_positive_feedback (1) The per-destination amount of delivery concurrency positive feedback, after a delivery completes without connection or handshake failure. ### transport_destination_concurrency_positive_feedback ($default_destination_concurrency_posi‐ ### tive_feedback) A transport-specific override for the default_destination_concurrency_positive_feed‐ back 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 performance analysis purposes. ## RECIPIENT SCHEDULING CONTROLS ### default_destination_recipient_limit (50) The default maximal number of recipients per message delivery. ### transport_destination_recipient_limit ($default_destination_recipient_limit) A transport-specific override for the default_destination_recipient_limit parameter value, where _transport_ is the master.cf name of the message delivery transport. ## MESSAGE SCHEDULING CONTROLS ### default_delivery_slot_cost (5) How often the Postfix queue manager's scheduler is allowed to preempt delivery of one message with another. ### transport_delivery_slot_cost ($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 ($default_minimum_delivery_slots) A transport-specific override for the default_minimum_delivery_slots parameter value, where _transport_ is the master.cf name of the message delivery transport. ### default_delivery_slot_discount (50) The default value for transport-specific _delivery_slot_discount settings. ### transport_delivery_slot_discount ($default_delivery_slot_discount) A transport-specific override for the default_delivery_slot_discount 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 ($default_delivery_slot_loan) A transport-specific override for the default_delivery_slot_loan parameter value, where _transport_ is the master.cf name of the message delivery transport. ## OTHER RESOURCE AND RATE CONTROLS ### minimal_backoff_time (300s) The minimal time between attempts to deliver a deferred message; prior to Postfix 2.4 the default value was 1000s. ### maximal_backoff_time (4000s) The maximal time between attempts to deliver a deferred message. ### maximal_queue_lifetime (5d) Consider a message as undeliverable, when delivery fails with a temporary error, and the time in the queue has reached the maximal_queue_lifetime limit. ### queue_run_delay (300s) The time between deferred queue scans by the queue manager; prior to Postfix 2.4 the default value was 1000s. ### transport_retry_time (60s) The time between attempts by the Postfix queue manager to contact a malfunctioning message delivery transport. Available in Postfix version 2.1 and later: ### bounce_queue_lifetime (5d) Consider a bounce message as undeliverable, when delivery fails with a temporary er‐ ror, and the time in the queue has reached the bounce_queue_lifetime limit. Available in Postfix version 2.5 and later: ### default_destination_rate_delay (0s) The default amount of delay that is inserted between individual message deliveries to the same destination and over the same message delivery transport. ### transport_destination_rate_delay ($default_destination_rate_delay) A transport-specific override for the default_destination_rate_delay parameter value, where _transport_ is the master.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, regardless of destination. ### transport_transport_rate_delay ($default_transport_rate_delay) A transport-specific override for the default_transport_rate_delay parameter value, where the initial _transport_ in the parameter name is the master.cf name of the message delivery transport. ## 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 information 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 Post‐ fix queue. ## MISCELLANEOUS CONTROLS ### config_directory (see 'postconf -d' output) The default location of the Postfix main.cf and master.cf configuration 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 logging sub-second delay values. ### helpful_warnings (yes) Log warnings about problematic configuration settings, and provide helpful sugges‐ tions. ### 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 exam‐ ple, "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 de‐ lay 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)](https://www.chedong.com/phpMan.php/man/trivial-rewrite/8/markdown), address routing [bounce(8)](https://www.chedong.com/phpMan.php/man/bounce/8/markdown), delivery status reports [postconf(5)](https://www.chedong.com/phpMan.php/man/postconf/5/markdown), configuration parameters [master(5)](https://www.chedong.com/phpMan.php/man/master/5/markdown), generic daemon options [master(8)](https://www.chedong.com/phpMan.php/man/master/8/markdown), process manager [postlogd(8)](https://www.chedong.com/phpMan.php/man/postlogd/8/markdown), Postfix logging [syslogd(8)](https://www.chedong.com/phpMan.php/man/syslogd/8/markdown), 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_(8postfix)](https://www.chedong.com/phpMan.php/man/QMGR/8postfix/markdown)