Email clients (like Thunderbird or Outlook) get logged out or suddenly do not have access to their mailbox.
Users have a bunch of different ways to authenticate to Dovecot. They might use any combination of “username” and “domain”:
Logging in with username@domain or just “username”.
Dovecot does not have the concepts of domains so above users are two different users for Dovecot. In UCS 4.2 there has been an issue with internal caching from Dovecot which caused the logouts. This has been fixed with UCS 4.3 or later.
Make sure your users all use “username@domain” as credentials for the IMAP service.
Set the Dovecot cache to zeor. Remember the value so you can set it to the previous value after the upgrade to UCS 4.3.
ucr get mail/dovecot/auth/cache_size ucr set mail/dovecot/auth/cache_size=0 $ service dovecot restart