Comment # 5 on bug 1166007 from Christian Boltz

(In reply to Michael Hirmke from comment #4)
> I get an error message from the dovecot master process
> "master: Error: serivce(lmtp): kill(<pid>, SIGINT) failed: Operation not
> permitted"
> This happens, when the lmtp service should be killed after idle timeout.
> There seems to be no entry in the audit.log for this error.
> Isn't this an error caused by apparmor, then?

It could be caused by AppArmor (maybe a missing "signal" rule), but in that
case you should see an audit.log entry for it. (Looking at the profiles,
sending a signal from /usr/sbin/dovecot to lmtp should already be allowed.)