SYNOPSIS
qmgr [generic Postfix daemon options]
DESCRIPTION
The qmgr 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
notifications.
MAIL QUEUES
The qmgr daemon maintains the following queues:
incoming
Inbound mail from the network, or mail picked up by the local
pickup agent 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 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 daemon is responsible for asking the bounce(8), defer(8) or
trace(8) daemons to send delivery reports.
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
deferred. The time interval between delivery attempts is dou-
bled 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,
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 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
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)
The qmgr 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 daemon does not talk to the outside
world, and it can be run at fixed low privilege in a chrooted environ-
ment.
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 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 smtpd. 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) processes
are persistent. 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
allow_min_user (no)
Allow a recipient address to have `-' as the first character.
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 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 (10000)
The default per-transport upper limit on the number of in-memory
recipients.
default_destination_concurrency_limit (20)
The default maximal number of parallel deliveries to the same
destination.
transport_destination_concurrency_limit ($default_destination_concur-
rency_limit)
Idem, for delivery via the named message transport.
RECIPIENT SCHEDULING CONTROLS
default_destination_recipient_limit (50)
The default maximal number of recipients per message delivery.
transport_destination_recipient_limit ($default_destination_recipi-
ent_limit)
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 ($default_delivery_slot_cost)
Idem, for delivery via the named message transport.
default_minimum_delivery_slots (3)
How many recipients a message must have in order to invoke the
Postfix queue manager's scheduling algorithm at all.
transport_minimum_delivery_slots ($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 ($default_delivery_slot_discount)
Idem, for delivery via the named message transport.
default_delivery_slot_loan (3)
The default value for transport-specific _delivery_slot_loan
settings.
transport_delivery_slot_loan ($default_delivery_slot_loan)
Idem, for delivery via the named message transport.
OTHER RESOURCE AND RATE CONTROLS
minimal_backoff_time (1000s)
The minimal time between attempts to deliver a deferred message.
maximal_backoff_time (4000s)
The maximal time between attempts to deliver a deferred message.
bounce_queue_lifetime (5d)
The maximal time a bounce message is queued before it is consid-
ered undeliverable.
MISCELLANEOUS CONTROLS
config_directory (see 'postconf -d' output)
The default location of the Postfix main.cf and master.cf con-
figuration files.
daemon_timeout (18000s)
How much time a Postfix daemon process may take to handle a
request before it is terminated by a built-in watchdog timer.
defer_transports (empty)
The names of message delivery transports that should not be
delivered to unless someone issues "sendmail -q" or equivalent.
helpful_warnings (yes)
Log warnings about problematic configuration settings, and pro-
vide helpful suggestions.
ipc_timeout (3600s)
The time limit for sending or receiving information over an
internal communication channel.
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 (postfix)
The mail system name that is prepended to the process name in
syslog records, so that "smtpd" becomes, for example, "post-
fix/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
AUTHOR(S)
Wietse Venema
IBM T.J. Watson Research
P.O. Box 704
Yorktown Heights, NY 10598, USA
Scheduler enhancements:
Patrik Rak
Modra 6
155 00, Prague, Czech Republic
QMGR(8)
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