This will hopefully be the last comment for this case: Obviously I messed up apparmor completely. So I removed apparmor.d and reinstalled all apparmor packages from scratch. Besides for dovecot I never modified any apparmor profile. Having done that, dovecot started to complain again for some actions. So I reran aa-logprof and got the modification/new profiles shown in the attachements. I hope, they will be helpful.