Dovecot submission protocol keeps getting turned back on after Debian upgrade

user1247280 asked:

I have dovecot imap server and exim4 running on Debian Buster. I am using exim4 for smtp, but at the Debian upgrade before last (early Jan 2021), Debian arbitrarily turned on submission in dovecot by adding the file /usr/share/dovecot/protocols.d/submissiond.protocol. That blocks exim from properly servicing smtp.

It took me ages to find this was the cause, but once I had, I renamed that file to submissiond.protocol.unused and all was well. However, I did a Debian upgrade again today (with apt) in response to a security alert in an unrelated package, and it put that file back again and broke smtp once more.

Clearly I am not turning this protocol off in the correct way. What should I do to turn it off in such a way it stays off over Debian upgrades?

My answer:

If you don’t need the Dovecot submission daemon, you can just remove the package that provided that functionality.

[email protected]:~$ sudo apt purge dovecot-submissiond 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 1,165 kB disk space will be freed.
Do you want to continue? [Y/n] 
(Reading database ... 39064 files and directories currently installed.)
Removing dovecot-submissiond (1: ...
Processing triggers for dovecot-core (1: ...
(Reading database ... 39057 files and directories currently installed.)
Purging configuration files for dovecot-submissiond (1: ...

If apt didn’t restart dovecot during the removal, you will need to do so yourself.

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