I'm migrating all my email content (including folder structure) from one gmail account to another. Both accounts are managed by the school where I work. They do not offer a data migration service and recommend to use Thunderbird. I was able to set up both accounts on thunderbird and download locally all the email content from the "origin account". I also managed to copy or move half of the email content from the "origin account" to the "destination account". However it has been a very slow process, since I often get the message that the connection timed out. I get this message regardless of the size or number of emails that I'm moving and/or copying (i.e. I got a "connection timed out" message moving a single email without attachments). I've tried to work offline, and while it seems that the emails have been copied (or moved - I've tried both), once I go back online the emails (or at least not all of them) are not downloaded to the "destination account". Any suggestion?