I've been trying to use Kerberos and PLAIN text file for authentication. I've setup deliver in postfix master.cf and make sure correct username are expanded but deliver is always told me "user unknown". I can logon into mailbox using Kerberos w/o problems and can send emails. Looks like Dovecot lookup up passwd files and not finding users which are in Kerberos realm.
# 1.0.15: /etc/dovecot/dovecot.conf log_path: /var/log/dovecot.log protocols: imap ssl_cert_file: /etc/postfix/new_chained.crt ssl_key_file: /etc/postfix/mail.pem login_dir: /var/run/dovecot/login login_executable: /usr/lib/dovecot/imap-login login_greeting_capability: yes mail_location: maildir:/var/mail/store/%u dotlock_use_excl: yes maildir_copy_with_hardlinks: yes auth default: mechanisms: PLAIN CRAM-MD5 GSSAPI passdb: driver: passwd-file args: /etc/dovecot/passwd userdb: driver: static args: uid=vmail gid=vmail home=/var/mail/store/%u socket: type: listen client: path: /var/spool/postfix/private/auth mode: 432 user: postfix group: postfix master: path: /var/run/dovecot/auth-master mode: 438 user: root group: root plugin: sieve: /var/mail/store/%u/sieve