User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.0.3) Gecko/2008101315 Linux Mint/6 (Felicia) Firefox/3.0.3 Build Identifier: 20080925 I used to have this problem in the past before I stopped using thunderbird, but having just tried again I've hit the same problem (so it's not anything new or specific to my build) If my home directory fills up, then thunderbird seems to 'forget' where it was in the mail box and downloads all messages from the server again resulting in duplicates (P.S. View->Sort By->Order Received is a great way to remove them!) My assumption would be that popstate.dat is updated in a way that is susceptible to losing data when updated i.e. it's not being updated 'inline' on the filesystem. The problem didn't appear to affect an IMAP mailbox that was live at the same time. Since this seems repeatable, I don't believe it's related to any of the other 'duplicate email' bugs in the system. Reproducible: Always Steps to Reproduce: 1. Use a POP3 mailbox with 'leave messages on server' 2. Fill up your home directory (or the file system where the mailbox is stored) 3. Try to retrieve new messages Actual Results: Entire mailbox was duplicated with messages from the server Expected Results: no duplicates, only new messages downloaded

Granted, this duplicate was a bit hard to find (took three separate searches).