Firs, I suggest highlighing account in folder pane, rightclick and select 'subscribe' and see if that menu shows the duplicates. My guess is that it will not. If all duplicate folders show duplicate content, try unsubscribing from duplicates. My next suggestion, IF THESE ARE IMAP ACCOUNTS, is to click help>troubleshooting information. Then, scroll to 'profile folder' and click 'open folder' Next, exit thunderbird Now, click the imapmail folder Now, click the imap account folder Next, delete all content here. Since this is an imap account, thunderbird will repopulate on a restart Restart thunderbird and see if the duplicates are still there.