Hi there,

After over a week of Dovecot 2.3 -> 2.4 upgrade testing in various mailserver clones, I am now ready for the big picture. Thanks Aki for the Config Upgrader https://dovecot.org/upgrader/ which helped a lot!

Tomorrow, I am planning to upgrade a larger mailserver in these 3 steps:

1. Debian Bullseye / Dovecot 2.3.21 => 2.4.1
2. Debian Bullseye => Bookworm / Dovecot 2.4.1 => 2.4.2
3. Debian Bookworm => Trixie

Postfix needs to talk to Dovecot over LMTP, using the following in main.cf:

virtual_transport = lmtp:unix:/run/dovecot/lmtp

Now, while testing this in a full server clone, I stepped over my planned LMTP server setup:

=============================================== service lmtp { unix_listener /run/dovecot/lmtp { mode = 0666 user = postfix group = postfix } }

protocols = imap pop3 sieve lmtp

The socket needs to be owned by postfix:postfix for some (security) reasons, otherwise Postfix complains. That's why I cannot go with the default, as documented here:

https://doc.dovecot.org/2.4.2/core/config/delivery/lmtp.html#lmtp-server

The UNIX listener on $base_dir/lmtp is enabled by default when protocols setting contains lmtp.

But, when using an absolute path on unix_listener, upgrade step 2) Bullseye=>Bookworm breaks with:

Processing triggers for dovecot-core (2:2.4.2-2+debian12) ... Job for dovecot.service failed because the control process exited with error code. (...) dovecot[34446]: master: Error: service(lmtp): Socket already exists: /var/run/dovecot/lmtp dovecot[34446]: master: Fatal: Failed to start listeners

I then moved to unix_listener lmtp:

service lmtp { unix_listener lmtp { mode = 0666 user = postfix group = postfix } }

Bookworm upgrade (restarted from scratch with a fresh server clone) went through fine. But even after several dovecot.service restarts, the socket ended up in /run/lmtp without creating the /run/dovecot directory, and after a full system reboot, it was suddenly back where I have expected it: /run/dovecot/lmtp I never changed base_dir, which defaults to /var/run/dovecot/

So, here's my question: Is that really the recommended setup (using inet_listener lmtp instead of an absolute path) and how can I trust Dovecot to always create the socket in $base_dir/lmtp as documented? Are you guys aware of this issue or was it just me, a temporary hiccup on my just upgraded server? I just found this in mail.log:

dovecot: master: Error: bind(/var/run/dovecot/lmtp) failed: No such file or directory dovecot: master: Error: service(lmtp): net_listen_unix(/var/run/dovecot/lmtp) failed: No such file or directory dovecot: master: Fatal: Failed to start listeners

Again, this problem seems to have occurred both with unix_listener /run/dovecot/lmtp and unix_listener lmtp and only resolved after a full system reboot.

Thanks, Philip