NAME
qmgr - Postfix queue managerSYNOPSIS
qmgr [generic Postfix daemon options]
DESCRIPTION
The 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 QUEUES
The 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 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 maintained by the trace(8) daemon.
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 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 destination.
- 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 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.
STANDARDS
RFC 3463 (Enhanced status codes) RFC 3464 (Delivery status notifications)
SECURITY
The daemon is not security sensitive. It reads single-character messages from untrusted local users, and thus may be susceptible to denial of service attacks. The daemon does not talk to the outside world, and it can be run at fixed low privilege in a chrooted environment.
DIAGNOSTICS
Problems and transactions are logged to syslogd(8) or postlogd(8). Corrupted message files are saved to the corrupt queue for further inspection.
BUGS
A single queue manager process has to compete for disk access with multiple 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 is a persistent process. Use the " postfix reload" command after a configuration change.
COMPATIBILITY CONTROLS
Available before Postfix version 2.5:
- allow_min_user (no)
- Allow a sender or recipient address to have `-' as the first character.
- 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 ($default_extra_recipient_limit)
- A transport-specific override for the default_extra_recipient_limit parameter value, where transport is the master.cf name of the message delivery transport.
- default_recipient_refill_limit (100)
- The default per-transport limit on the number of recipients refilled at once.
- transport_recipient_refill_limit ($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 ($default_recipient_refill_delay)
- A transport-specific override for the default_recipient_refill_delay parameter value, where transport is the master.cf name of the message delivery transport.
DELIVERY CONCURRENCY CONTROLS
- initial_destination_concurrency (5)
- The initial per-destination concurrency level for parallel delivery to the same destination.
- default_destination_concurrency_limit (20)
- The default maximal number of parallel deliveries to the same destination.
- transport_destination_concurrency_limit ($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.
- 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_concurrency_failed_cohort_limit)
- A transport-specific override for the default_destination_concurrency_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 handshake failure.
- transport_destination_concurrency_negative_feedback ($default_destination_concurrency_negative_feedback)
- A transport-specific override for the default_destination_concurrency_negative_feedback parameter value, where transport is the master.cf name of the message delivery transport.
- default_destination_concurrency_positive_feedback (1)
- The per-destination amount of delivery concurrency positive feedback, after a delivery completes without connection or handshake failure.
- transport_destination_concurrency_positive_feedback ($default_destination_concurrency_positive_feedback)
- A transport-specific override for the default_destination_concurrency_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 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 ($default_delivery_slot_loan)
- A transport-specific override for the default_delivery_slot_loan parameter value, where transport is the master.cf name of the message delivery transport.
OTHER RESOURCE AND RATE CONTROLS
- minimal_backoff_time (300s)
- The minimal time between attempts to deliver a deferred message; prior to Postfix 2.4 the default value was 1000s.
- maximal_backoff_time (4000s)
- The maximal time between attempts to deliver a deferred message.
- maximal_queue_lifetime (5d)
- Consider a message as undeliverable, when delivery fails with a temporary error, and the time in the queue has reached the maximal_queue_lifetime limit.
- queue_run_delay (300s)
- The time between deferred queue scans by the queue manager; prior to Postfix 2.4 the default value was 1000s.
- transport_retry_time (60s)
- The time between attempts by the Postfix queue manager to contact a malfunctioning message delivery transport.
- bounce_queue_lifetime (5d)
- Consider a bounce message as undeliverable, when delivery fails with a temporary error, and the time in the queue has reached the bounce_queue_lifetime limit.
- default_destination_rate_delay (0s)
- The default amount of delay that is inserted between individual message deliveries to the same destination and over the same message delivery transport.
- transport_destination_rate_delay ($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.
- 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.
- 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 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 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".
- confirm_delay_cleared (no)
- After sending a "your message is delayed" notification, inform the sender when the delay clears up.
- service_name (read-only)
- The master.cf service name of a Postfix daemon process.
- 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