I installed Thunderbird a few weeks ago and I'm now trying to migrate from Windows Live Mail 2012 (WLM) to Thunderbird (TB). I am connected to a server called Copper..net via IMAP. (I've set up 2 other email accounts under TB, one of which I will almost certainly abandon and the other, I hope, will become my default server. But right now, I'm not really using either). Most of my emails -- I have over 300,000 -- are stored in local folders. When mail comes into my Inbox, I generally either delete it, mark it as junk, or once read, store it in a local file. Until yesterday, all of my IMAP folders showed up under the Copper.net account. They also showed up when I went to File subscribe and refreshed the list (other than one episode which I was able to resolve). Now, they don't show up in either place. They still do show up normally in the other accounts. Since installing Thunderbird, I have managed to transfer most of my local emails from WLM to TB, so I am now down to 3 of my largest folders, containing between 60,000 and 65,000 emails each. Two days ago, I was able to transfer one of them, albeit with considerable difficulties along the way. My method was to set up a new IMAP folder called Transfers. I COPY emails from the WLM folder to it (in chunks for larger folders). Then MOVE the emails from the TB Transfers folder to the TB local folder. When everything is working properly, that move eventually results in the TB transfer folder being empty, which then results in the WLM transfer folder being empty. And then I can restart the process. If for some reason, the move does NOT empty the transfer folder, I do so manually by deleting all the emails and then emptying the trash. I then check properties to make sure that the folder is really empty, and if it isn't, use the tools under properties in WLM to manually delete them Yesterday, when I tried to do all this again for my 2nd large folder, I found that the transfer box in TB a) often didn't contain all the emails it should have and b) that the ones that showed up as being there wouldn't move at all. I tried compacting, repairing, getting messages, all to force syncing , but nothing worked. And this morning, things went from bad to worse because now my IMAP folders no longer show up at all (except Inbox and Trash). During this whole time, the inbox has been syncing properly and mostly, promptly. Finally, I should add that I did download and add the import/export NG tool and while it worked pretty successfully for small folders, if did not work well for larger ones. I'm still in dialogue with the developer. Any help would be much appreciated; I'm incredibly frustrated. P.S. I tried this morning to repair TB, just in case, but using Control Panel, the only option was to uninstall it, which I did not want to do. I do wonder whether TB has somehow gotten corrupted. I also tried opening in safe mode, which didn't help. I shut my computer off at night, so it's restarted at least once a day. Yesterday and today, I also restarted during the day in hopes that it might help. No dice.