i have a problem with postfix. I now have a freshly installed Ubuntu 18.04. I install Postfix and during the installation, I say that the mails should go out via a relay. Because the proxy accepts only one domain as a sender, I need a rewrite for sender Mail so I added this line to main.cf:

sender_canonical_classes = envelope_sender, header_sender
sender_canonical_maps =  regexp:/etc/postfix/sender_canonical_maps
smtp_header_checks = regexp:/etc/postfix/header_check
# cat /etc/postfix/sender_canonical_maps
/.+/    [email protected]
# cat /etc/postfix/header_check
/From:.*/ REPLACE From: [email protected]

Otherwise I don't even touch the configuration. Postfix also runs for the first time and I can test everything successfully.

It can run for a few minutes or even hours. But at some point Postfix just turns itself off.

See log:

# tail -f /var/log/mail.log
Jun  3 09:20:06 my-server postfix/postfix-script[11813]: refreshing the Postfix mail system
Jun  3 09:20:06 my-server postfix/master[7467]: reload -- version 3.3.0, configuration /etc/postfix
Jun  3 09:24:07 my-server postfix/pickup[11826]: 9C62E4209A: uid=33 from=<[email protected]>
Jun  3 09:24:07 my-server postfix/cleanup[11858]: 9C62E4209A: message-id=<JRKi3qQ2QaLr7QtriyHqTzCrODX1JYZ5wh7S1ED9o@umfragen.testbed.gdi-de.org>
Jun  3 09:24:07 my-server postfix/qmgr[11824]: 9C62E4209A: from=<[email protected]>, size=3230, nrcpt=1 (queue active)
Jun  3 09:24:07 my-server postfix/smtp[11860]: 9C62E4209A: replace: header From: Test <[email protected]>: From: [email protected]
Jun  3 09:24:07 my-server postfix/smtp[11860]: 9C62E4209A: to=<[email protected]>, relay=my.proxy[IP.IP.IP.IP]:25, delay=0.07, delays=0.02/0.01/0.01/0.02, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as A836F285F)
Jun  3 09:24:07 my-server postfix/qmgr[11824]: 9C62E4209A: removed
Jun  3 10:31:06 my-server postfix/postfix-script[20360]: stopping the Postfix mail system
Jun  3 10:31:06 my-server postfix/master[7467]: terminating on signal 15

You see at this log, that I have testet everything and at jun 3 10:31 postfix is turned off.

So if I try now to start it, the service is "masked"

# service postfix start
Failed to start postfix.service: Unit postfix.service is masked.
# systemctl start postfix
Failed to start postfix.service: Unit postfix.service is masked.

If I try to unmask Postfix. It works, but Postfix is ​​not addressable.

# systemctl unmask postfix.service
Removed /etc/systemd/system/postfix.service.
# systemctl start postfix
# systemctl status postfix
● postfix.service - LSB: Postfix Mail Transport Agent
   Loaded: loaded (/etc/init.d/postfix; generated)
   Active: active (exited) since Fri 2020-06-05 13:59:57 CEST; 11s ago
     Docs: man:systemd-sysv-generator(8)
  Process: 17347 ExecStart=/etc/init.d/postfix start (code=exited, status=0/SUCCESS)
 Main PID: 7472 (code=exited, status=0/SUCCESS)

Jun 05 13:59:57 my-server systemd[1]: Starting LSB: Postfix Mail Transport Agent...
Jun 05 13:59:57 my-server systemd[1]: Started LSB: Postfix Mail Transport Agent.
# telnet localhost 25
telnet: Unable to connect to remote host: Connection refused

For this progress, there are no new entries in the mail.log and mail.err

The only way to get it run again is to remove it clear apt and install postfix again. But after a few minutes or hours, the postfix service turned off again.

At this point I have exhausted my knowledge on this.

  • Anyone? I have a similar problem on Debian 11. Postfix runs after installing it, netstat shows it is listening on port 25, but after the first reboot it is suddenly masked. Even after unmasking, it won't work anymore. It just starts and immediately stops, doesn't start listening on port 25 anymore.
    – Luc VdV
    Sep 7, 2021 at 11:26

1 Answer 1


You can unmask and restart service

systemctl unmask postfix.service
  • This (old) question relates to a generated (see the "systemd-sysv-generator" note) unit, so making changes on the systemd side is unlikely to properly diagnose or resolve the SysV-derived unit status.
    – anx
    Oct 23, 2022 at 4:16

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