Problem :
Sporadically Thunderbird would get stuck on “Checking inbox for New Messages”. Whatever you do, the new messages are not downloaded. It gets past the logging in so you know it has logged to your mail server and is waiting for the server to send it the list of new mails.
Solution : None that I have found. Tried everything but nothing works.
Workaround : If you have webmail access, login with webmail. Move your inbox emails to a temp folder. then half them back to inbox and then another half to your inbox. It works