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 pro‐
cesses. 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 direc‐
tory.
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 back‐
off 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 sta‐
tus 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.
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 cor‐
rect 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 col‐
lapsed 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.
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 $default_fil‐
ter_nexthop instead; when that value is empty, use the domain in the recipient address.
ACTIVE QUEUE CONTROLS
qmgr_clog_warn_time (300s)
The minimal delay between warnings that a specific destination is clogging up the Postfix active queue.
qmgr_message_active_limit (20000)
The maximal number of messages in the active queue.
qmgr_message_recipient_limit (20000)
The maximal number of recipients held in memory by the Postfix queue manager, and the maximal size of
the short-term, in-memory "dead" destination status cache.
qmgr_message_recipient_minimum (10)
The minimal number of in-memory recipients for any message.
default_recipient_limit (20000)
The default per-transport upper limit on the number of in-memory recipients.
transport_recipient_limit ($default_recipient_limit)
Idem, for delivery via the named message 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 ($default_extra_recipient_limit)
Idem, for delivery via the named message transport.
Available in Postfix version 2.4 and later:
default_recipient_refill_limit (100)
The default per-transport limit on the number of recipients refilled at once.
transport_recipient_refill_limit ($default_recipient_refill_limit)
Idem, for delivery via the named message transport.
default_recipient_refill_delay (5s)
The default per-transport maximum delay between recipients refills.
transport_recipient_refill_delay ($default_recipient_refill_delay)
Idem, for delivery via the named message transport.
transport_initial_destination_concurrency ($initial_destination_concurrency)
Initial concurrency for delivery via the named message 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 ($default_destination_concurrency_failed_cohort_limit)
Idem, for delivery via the named message transport.
default_destination_concurrency_negative_feedback (1)
The per-destination amount of delivery concurrency negative feedback, after a delivery completes with a
connection or handshake failure.
transport_destination_concurrency_negative_feedback ($default_destination_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 with‐
out connection or handshake failure.
transport_destination_concurrency_positive_feedback ($default_destination_concurrency_positive_feedback)
Idem, for delivery via the named message transport.
destination_concurrency_feedback_debug (no)
Make the queue manager's feedback algorithm verbose for performance analysis purposes.
RECIPIENT SCHEDULING CONTROLS
default_destination_recipient_limit (50)
The default maximal number of recipients per message delivery.
transport_destination_recipient_limit ($default_destination_recipient_limit)
Idem, for delivery via the named message 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 ($default_delivery_slot_cost)
Idem, for delivery via the named message transport.
default_minimum_delivery_slots (3)
How many recipients a message must have in order to invoke the Postfix queue manager's scheduling algo‐
rithm at all.
transport_minimum_delivery_slots ($default_minimum_delivery_slots)
Idem, for delivery via the named message transport.
default_delivery_slot_discount (50)
The default value for transport-specific _delivery_slot_discount settings.
transport_delivery_slot_discount ($default_delivery_slot_discount)
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 contact 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 considered 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; the
resulting behavior depends on the value of the corresponding per-destination recipient limit.
transport_destination_rate_delay $default_destination_rate_delay
Idem, for delivery via the named message 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.
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.
for example, "postfix/smtpd".
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
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
QMGR(8)
Back to main site | Back to man page index