I configured my Hotmail account with Thunderbird 38.1.0. After downloading all of my emails from the server, I tried to archive all my email from 2007 (about 1300 messages). Thunderbird moved the local mails to an archive folder, and succeeded to create the archive folder in Hotmail and create the mails there, but failed to delete the mails from the inbox. So, next thing Thunderbird does is redownload all of the deleted mails, since its trying to synchronize the inbox with the server. Up to this point it wouln't be so bad. I'd just have to delete the archive folder and retry. But then, it looks like Thunderbird retries the operation, getting the same result, and adding duplicates of all the messages in the archive folder (both locally and remotely). Even worse, it won't stop retrying, so the longer I keep it open the more it duplicates the mails in the archive folder.