Mail server was recently upgraded (from G4 to G5), but stayed at 10.4.11. The first few days were fine, but then we ran into some problems with db errors. A full reconstruct of the databases seemed to resolve the issues we were seeing then (actually- it did. We have not seen more db errors).

However, we are now running into a problem where the users are locked out of their mail boxes-the logs show a whole host of these entries all at once, for multiple users:
mail pop3[8750]: Unable to lock maildrop for userz: Mailbox is locked by POP server

Okay- a normal thing under most circumstances- a lock prevents two clients from editing the files at the same time, no big deal. However, what we are seeing now is a whole group of users that gets locked, and so none of them can get mail. And the locks don’t disappear after a timeout period (ten minutes I thought)- once the machine decides they are locked the mailboxes stay locked. A reboot of the server is the only way to get around it (restarting the mail service doesn’t do it). Even IMAP users don’t have access to email when this occurs.

Now, we don’t see anything obvious in the mail logs happening before the messages get locked, and we don’t see anything sticking out like a sore thumb in the other general logs. Any ideas on what might be a potential cause of this issue?