I added an old Gmail account to my Thunderbird app on my Mac (newish MacBook Pro with Mavericks). I checked "Keep messages for this account on this computer" in the "Synchronization & Storage" section of Account Settings. I ended up with an archive folder that was 285GB! It took me nearly a month to figure out why my hard disk space was suddenly disappearing. . . Mavericks hides the Library folder, so it was hard to even find the archive file. Anyway, I unchecked the "Keep messages for this account on this computer" setting and the archive file quickly went down to 192GB. However, according to my hosting provider, the other IMAP address I have on Thunderbird is only 6GB in size. I have the box checked for that account, and I do want to locally archive that address. How do I get rid of all of this extra email archive? I don't need nearly 200GB of archived email!!!! My local hard drive is only 500GB!