No, I have two instances of mailcow running, one still @ 11/24 and this one has this log:
Connect from 172.22.1.8#015
dovecot: lmtp(124754): Disconnect from 172.22.1.8: Logged out (state=MAIL FROM)#015
This seems (at least from my point of view) not as problematic.
I just hope that watchdog does not trigger netfilter/fail2ban to blacklist itself.
The “unknown user” message is a fail2ban message for the dovecot filter