1QMGR(8) System Manager's Manual QMGR(8)
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6 qmgr - Postfix queue manager
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9 qmgr [generic Postfix daemon options]
10
12 The qmgr(8) daemon awaits the arrival of incoming mail and arranges for
13 its delivery via Postfix delivery processes. The actual mail routing
14 strategy is delegated to the trivial-rewrite(8) daemon. This program
15 expects to be run from the master(8) process manager.
16 Mail addressed to the local double-bounce address is logged and dis‐
18 carded. This stops potential loops caused by undeliverable bounce
19 notifications.
20
22 The qmgr(8) daemon maintains the following queues:
23 incoming
25 Inbound mail from the network, or mail picked up by the local
26 pickup(8) daemon from the maildrop directory.
27 active Messages that the queue manager has opened for delivery. Only a
29 limited number of messages is allowed to enter the active queue
30 (leaky bucket strategy, for a fixed delivery rate).
31 deferred
33 Mail that could not be delivered upon the first attempt. The
34 queue manager implements exponential backoff by doubling the
35 time between delivery attempts.
36 corrupt
38 Unreadable or damaged queue files are moved here for inspection.
39 hold Messages that are kept "on hold" are kept here until someone
41 sets them free.
42
44 The qmgr(8) daemon keeps an eye on per-message delivery status reports
45 in the following directories. Each status report file has the same name
46 as the corresponding message file:
47 bounce Per-recipient status information about why mail is bounced.
49 These files are maintained by the bounce(8) daemon.
50 defer Per-recipient status information about why mail is delayed.
52 These files are maintained by the defer(8) daemon.
53 trace Per-recipient status information as requested with the Postfix
55 "sendmail -v" or "sendmail -bv" command. These files are main‐
56 tained by the trace(8) daemon.
57 The qmgr(8) daemon is responsible for asking the bounce(8), defer(8) or
59 trace(8) daemons to send delivery reports.
60
62 The queue manager implements a variety of strategies for either opening
63 queue files (input) or for message delivery (output).
64 leaky bucket
66 This strategy limits the number of messages in the active queue
67 and prevents the queue manager from running out of memory under
68 heavy load.
69 fairness
71 When the active queue has room, the queue manager takes one mes‐
72 sage from the incoming queue and one from the deferred queue.
73 This prevents a large mail backlog from blocking the delivery of
74 new mail.
75 slow start
77 This strategy eliminates "thundering herd" problems by slowly
78 adjusting the number of parallel deliveries to the same destina‐
79 tion.
80 round robin
82 The queue manager sorts delivery requests by destination.
83 Round-robin selection prevents one destination from dominating
84 deliveries to other destinations.
85 exponential backoff
87 Mail that cannot be delivered upon the first attempt is
88 deferred. The time interval between delivery attempts is dou‐
89 bled after each attempt.
90 destination status cache
92 The queue manager avoids unnecessary delivery attempts by main‐
93 taining a short-term, in-memory list of unreachable destina‐
94 tions.
95 preemptive message scheduling
97 The queue manager attempts to minimize the average per-recipient
98 delay while still preserving the correct per-message delays,
99 using a sophisticated preemptive message scheduling.
100
102 On an idle system, the queue manager waits for the arrival of trigger
103 events, or it waits for a timer to go off. A trigger is a one-byte mes‐
104 sage. Depending on the message received, the queue manager performs
105 one of the following actions (the message is followed by the symbolic
106 constant used internally by the software):
107 D (QMGR_REQ_SCAN_DEFERRED)
109 Start a deferred queue scan. If a deferred queue scan is
110 already in progress, that scan will be restarted as soon as it
111 finishes.
112 I (QMGR_REQ_SCAN_INCOMING)
114 Start an incoming queue scan. If an incoming queue scan is
115 already in progress, that scan will be restarted as soon as it
116 finishes.
117 A (QMGR_REQ_SCAN_ALL)
119 Ignore deferred queue file time stamps. The request affects the
120 next deferred queue scan.
121 F (QMGR_REQ_FLUSH_DEAD)
123 Purge all information about dead transports and destinations.
124 W (TRIGGER_REQ_WAKEUP)
126 Wakeup call, This is used by the master server to instantiate
127 servers that should not go away forever. The action is to start
128 an incoming queue scan.
129 The qmgr(8) daemon reads an entire buffer worth of triggers. Multiple
131 identical trigger requests are collapsed into one, and trigger requests
132 are sorted so that A and F precede D and I. Thus, in order to force a
133 deferred queue run, one would request A F D; in order to notify the
134 queue manager of the arrival of new mail one would request I.
135
137 RFC 3463 (Enhanced status codes)
138 RFC 3464 (Delivery status notifications)
139
141 The qmgr(8) daemon is not security sensitive. It reads single-character
142 messages from untrusted local users, and thus may be susceptible to
143 denial of service attacks. The qmgr(8) daemon does not talk to the out‐
144 side world, and it can be run at fixed low privilege in a chrooted
145 environment.
146
148 Problems and transactions are logged to the syslog daemon. Corrupted
149 message files are saved to the corrupt queue for further inspection.
150 Depending on the setting of the notify_classes parameter, the postmas‐
152 ter is notified of bounces and of other trouble.
153
155 A single queue manager process has to compete for disk access with mul‐
156 tiple front-end processes such as cleanup(8). A sudden burst of inbound
157 mail can negatively impact outbound delivery rates.
158
160 Changes to main.cf are not picked up automatically as qmgr(8) is a per‐
161 sistent process. Use the "postfix reload" command after a configuration
162 change.
163 The text below provides only a parameter summary. See postconf(5) for
165 more details including examples.
166 In the text below, transport is the first field in a master.cf entry.
168
170 Available before Postfix version 2.5:
171 allow_min_user (no)
173 Allow a sender or recipient address to have `-' as the first
174 character.
175
177 qmgr_clog_warn_time (300s)
178 The minimal delay between warnings that a specific destination
179 is clogging up the Postfix active queue.
180 qmgr_message_active_limit (20000)
182 The maximal number of messages in the active queue.
183 qmgr_message_recipient_limit (20000)
185 The maximal number of recipients held in memory by the Postfix
186 queue manager, and the maximal size of the size of the short-
187 term, in-memory "dead" destination status cache.
188 qmgr_message_recipient_minimum (10)
190 The minimal number of in-memory recipients for any message.
191 default_recipient_limit (20000)
193 The default per-transport upper limit on the number of in-memory
194 recipients.
195 transport_recipient_limit ($default_recipient_limit)
197 Idem, for delivery via the named message transport.
198 default_extra_recipient_limit (1000)
200 The default value for the extra per-transport limit imposed on
201 the number of in-memory recipients.
202 transport_extra_recipient_limit ($default_extra_recipient_limit)
204 Idem, for delivery via the named message transport.
205 Available in Postfix version 2.4 and later:
207 default_recipient_refill_limit (100)
209 The default per-transport limit on the number of recipients
210 refilled at once.
211 transport_recipient_refill_limit ($default_recipient_refill_limit)
213 Idem, for delivery via the named message transport.
214 default_recipient_refill_delay (5s)
216 The default per-transport maximum delay between recipients
217 refills.
218 transport_recipient_refill_delay ($default_recipient_refill_delay)
220 Idem, for delivery via the named message transport.
221
223 initial_destination_concurrency (5)
224 The initial per-destination concurrency level for parallel
225 delivery to the same destination.
226 default_destination_concurrency_limit (20)
228 The default maximal number of parallel deliveries to the same
229 destination.
230 transport_destination_concurrency_limit ($default_destination_concur‐
232 rency_limit)
233 Idem, for delivery via the named message transport.
234 Available in Postfix version 2.5 and later:
236 transport_initial_destination_concurrency ($initial_destination_concur‐
238 rency)
239 Initial concurrency for delivery via the named message trans‐
240 port.
241 default_destination_concurrency_failed_cohort_limit (1)
243 How many pseudo-cohorts must suffer connection or handshake
244 failure before a specific destination is considered unavailable
245 (and further delivery is suspended).
246 transport_destination_concurrency_failed_cohort_limit ($default_desti‐
248 nation_concurrency_failed_cohort_limit)
249 Idem, for delivery via the named message transport.
250 default_destination_concurrency_negative_feedback (1)
252 The per-destination amount of delivery concurrency negative
253 feedback, after a delivery completes with a connection or hand‐
254 shake failure.
255 transport_destination_concurrency_negative_feedback ($default_destina‐
257 tion_concurrency_negative_feedback)
258 Idem, for delivery via the named message transport.
259 default_destination_concurrency_positive_feedback (1)
261 The per-destination amount of delivery concurrency positive
262 feedback, after a delivery completes without connection or hand‐
263 shake failure.
264 transport_destination_concurrency_positive_feedback ($default_destina‐
266 tion_concurrency_positive_feedback)
267 Idem, for delivery via the named message transport.
268 destination_concurrency_feedback_debug (no)
270 Make the queue manager's feedback algorithm verbose for perfor‐
271 mance analysis purposes.
272
274 default_destination_recipient_limit (50)
275 The default maximal number of recipients per message delivery.
276 transport_destination_recipient_limit ($default_destination_recipi‐
278 ent_limit)
279 Idem, for delivery via the named message transport.
280
282 default_delivery_slot_cost (5)
283 How often the Postfix queue manager's scheduler is allowed to
284 preempt delivery of one message with another.
285 transport_delivery_slot_cost ($default_delivery_slot_cost)
287 Idem, for delivery via the named message transport.
288 default_minimum_delivery_slots (3)
290 How many recipients a message must have in order to invoke the
291 Postfix queue manager's scheduling algorithm at all.
292 transport_minimum_delivery_slots ($default_minimum_delivery_slots)
294 Idem, for delivery via the named message transport.
295 default_delivery_slot_discount (50)
297 The default value for transport-specific _delivery_slot_discount
298 settings.
299 transport_delivery_slot_discount ($default_delivery_slot_discount)
301 Idem, for delivery via the named message transport.
302 default_delivery_slot_loan (3)
304 The default value for transport-specific _delivery_slot_loan
305 settings.
306 transport_delivery_slot_loan ($default_delivery_slot_loan)
308 Idem, for delivery via the named message transport.
309
311 minimal_backoff_time (300s)
312 The minimal time between attempts to deliver a deferred message;
313 prior to Postfix 2.4 the default value was 1000s.
314 maximal_backoff_time (4000s)
316 The maximal time between attempts to deliver a deferred message.
317 maximal_queue_lifetime (5d)
319 The maximal time a message is queued before it is sent back as
320 undeliverable.
321 queue_run_delay (300s)
323 The time between deferred queue scans by the queue manager;
324 prior to Postfix 2.4 the default value was 1000s.
325 transport_retry_time (60s)
327 The time between attempts by the Postfix queue manager to con‐
328 tact a malfunctioning message delivery transport.
329 Available in Postfix version 2.1 and later:
331 bounce_queue_lifetime (5d)
333 The maximal time a bounce message is queued before it is consid‐
334 ered undeliverable.
335 Available in Postfix version 2.5 and later:
337 default_destination_rate_delay (0s)
339 The default amount of delay that is inserted between individual
340 deliveries to the same destination; with per-destination recipi‐
341 ent limit > 1, a destination is a domain, otherwise it is a
342 recipient.
343 transport_destination_rate_delay $default_destination_rate_delay
345 Idem, for delivery via the named message transport.
346
348 config_directory (see 'postconf -d' output)
349 The default location of the Postfix main.cf and master.cf con‐
350 figuration files.
351 defer_transports (empty)
353 The names of message delivery transports that should not deliver
354 mail unless someone issues "sendmail -q" or equivalent.
355 delay_logging_resolution_limit (2)
357 The maximal number of digits after the decimal point when log‐
358 ging sub-second delay values.
359 helpful_warnings (yes)
361 Log warnings about problematic configuration settings, and pro‐
362 vide helpful suggestions.
363 ipc_timeout (3600s)
365 The time limit for sending or receiving information over an
366 internal communication channel.
367 process_id (read-only)
369 The process ID of a Postfix command or daemon process.
370 process_name (read-only)
372 The process name of a Postfix command or daemon process.
373 queue_directory (see 'postconf -d' output)
375 The location of the Postfix top-level queue directory.
376 syslog_facility (mail)
378 The syslog facility of Postfix logging.
379 syslog_name (see 'postconf -d' output)
381 The mail system name that is prepended to the process name in
382 syslog records, so that "smtpd" becomes, for example, "post‐
383 fix/smtpd".
384
386 /var/spool/postfix/incoming, incoming queue
387 /var/spool/postfix/active, active queue
388 /var/spool/postfix/deferred, deferred queue
389 /var/spool/postfix/bounce, non-delivery status
390 /var/spool/postfix/defer, non-delivery status
391 /var/spool/postfix/trace, delivery status
392
394 trivial-rewrite(8), address routing
395 bounce(8), delivery status reports
396 postconf(5), configuration parameters
397 master(5), generic daemon options
398 master(8), process manager
399 syslogd(8), system logging
400
402 Use "postconf readme_directory" or "postconf html_directory" to locate
403 this information.
404 SCHEDULER_README, scheduling algorithm
405 QSHAPE_README, Postfix queue analysis
406
408 The Secure Mailer license must be distributed with this software.
409
411 Wietse Venema
412 IBM T.J. Watson Research
413 P.O. Box 704
414 Yorktown Heights, NY 10598, USA
415 Preemptive scheduler enhancements:
417 Patrik Rak
418 Modra 6
419 155 00, Prague, Czech Republic
420 QMGR(8)