Upgraded Ubuntu from 14.04lts to 16.04lts, having problems with dovecot, which ran fine under 14.04. Exim4 mail server running fine (receiving and delivering).Purged the dovecot install and deleted /etc/dovecot; reinstalled and disabled imap and configured required ssl (plus certificate) for imaps, set logfile to /var/log/dovecot. I've also enabled all verbose dovecot logging.No apparmor denied messages (the only dovecot messages in syslog and kern.log are for apparmor, there are no dovecot messages in /var/log/mail.log), but /var/log/dovecot contains:Jul 31 16:21:23 master: Info: Dovecot v2.2.22 (fe789d2) starting up for imap (core dumps disabled)Jul 31 16:21:31 master: Fatal: execv(/usr/lib/dovecot/imap-login) failed: Permission deniedJul 31 16:21:31 master: Error: service(imap-login): command startup failed, throttling for 2 secsJul 31 16:21:31 imap-login: Fatal: master: service(imap-login): child 16741 returned error 84 (exec() failed)Jul 31 16:21:33 master: Fatal: execv(/usr/lib/dovecot/imap-login) failed: Permission deniedJul 31 16:21:33 master: Error: service(imap-login): command startup failed, throttling for 4 secs...etc, repeats...systemctl seems ok:%> systemctl status dovecot.socket dovecot.socket - Dovecot IMAP/POP3 email server activation socket   Loaded: loaded (/etc/systemd/system/dovecot.socket; enabled; vendor preset: enabled)   Active: active (running) since Sun 2016-07-31 16:21:23 CDT; 8min ago   Listen: 0.0.0.0:993 (Stream)           [::]:993 (Stream)Jul 31 16:21:23 xxxxx systemd[1]: Listening on Dovecot IMAP/POP3 email server activation socket.Permissions:%> ls -l /usr/lib/dovecot/imap-login-rwxr-xr-x 1 root root 31K Apr  5 08:45 /usr/lib/dovecot/imap-login*I cannot figure out from the various logs what is actually not working. How can I identify where the configuration problem is?
dovecot /usr/lib/dovecot/imap-login failed: Permission denied
email;dovecot;imap