Quick summary: I am trying to copy all my Thunderbird messages to Google Mail. I set up a new account synced to my Google Mail account with IMAP, and disabled the POP syncing on the old, local account. Some messages were moved to the new account but not deleted from the old account. Is there a way to quickly delete messages from my local account that have already been moved? Background: The first problem I encountered is that attempts to move a large number of messages would often fail to finish, with a "could not parse command" error. After many attempts, I find that I now have many messages that were copied to the new IMAP account but not removed from the old local account. Is there a way to identify all messages in a given folder that have been copied to the account that is IMAPed? I would like to either delete these from the local account or at least move them to a "moved" folder so I can separate the messages that have been moved from those that still must be. Thank you.