I use Mail.app on 4 different computers to access the same mailboxes. I see the same problem on all of them --- if the Mail.app is running, then it catches all of the mail updates. But if a machine is turned off, when it turns back on the mailbox doesn't synchronize properly. I might delete 20 mail messages on one system and they are still on system #2 until I "rebuild."
I have seen this happen with the Mobile Me IMAP server, with Gmail, with courier IMAP, and with dovecot.
Does anybody else see this?
What should I do?
Is there a mail server that this happens less with?
It's very frustrating, as I get 200-300 mail messages a day and frequently end up handling email messages multiple times.