Ubuntu Manpage: qmgr - Postfix queue manager

Provided by: postfix_3.3.0-1ubuntu0.4_amd64

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 discarded.  This stops potential loops
       caused by undeliverable bounce notifications.

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 maintained 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 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.

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 denial of service attacks. The qmgr(8) 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 the syslog daemon.  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). 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 persistent 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_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 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.

       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_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.

       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  deliveries  to  the same
              destination; the resulting behavior depends on the  value  of  the  corresponding  per-destination
              recipient limit.

       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 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 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".

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.

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

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)