I'm running a server with Dovecot and Postfix. I'm seeing the following error in my log file: Unable to lock for exclusive access: Resource temporarily unavailable. How do I resolve this?
Mbox format is problematic in this way. You should upgrade to a newer Dovecot version (v2.x). The newer versions do some extra work to unlock the mbox earlier with POP3. Alternatively, you could switch to Maildir format where this isn't a problem. Either of these suggestions will resolve the issue.