Karl Davenport put forth on 9/22/2010 11:24 AM:
Running Dovecot version 1.0.10 on Ubuntu Server 8.04 amd64 (ext3).
Some users have emails that will not go away. They delete them and the message is moved to the trash folder only to reappear when the mailbox is refreshed. Moving the message manually to another folder has the same effect. We are running Thunderbird as our email client, though I have tried using other clients to remove the messages.
IIRC, by default, Thunderbird only performs expunge and trash folder emptying upon exit (though it's configurable with a check box), so anything in the trash will be there until closing TB. If you'd like emails to be deleted immediately, set "When I delete a message:" to "Remove it immediately" in the "Tools->Account Settings->Server Settings" tab _instead of_ "Move it to this folder [Trash]".
Also, worthy of note, is that TB's "Trash" is a local folder by default, NOT an IMAP folder. So if the trash isn't emptying properly, it can't be a Dovecot issue, as the Trash folder is on the local hard disk (unless some genius admin relocated everyone's Trash folder to IMAP storage or a network share via some ill advised group policy etc).
-- Stan