I read through the thread on Stale imap process and would like to
chime in that I too am having the problem. The only imap user on the
system is using Mail.app 2.1. The other users are using pop with
thunderbird. After quiting mail.app and stopping dovecot I can still
see many imap sessions opened. Over the course of the day a good
number of imap process will be open and no one will be able to
connect to the server via imap or pop. Typically I have to restart
dovecot twice a day with the following:

/etc/init.d/dovecot stop killall imap /etc/init.d/dovecot start

I've narrowed it down to an imap issue. If i don't connect with imap
the other users don't report any issues connecting with pop.

I'm using mbox as my mail format on centos 4. I know that the default
version on centos4 is .99, but it appears that people are still
having issues into 1.0rc2.

Could it have something to do with using mbox format?

Mike. mbond@the-forgotten.org