dchavenga, have you tried start Thunderbird ("TB") in safe mode ? see this support article TB works only in safe mode,

safe mode in mac;

• to open a terminal window, Cmd+space, type "terminal" and hit return
• assuming that TB is installed in the default applications directory, paste this command line (within quotes, not the quotes) "/Applications/­Thunderbird.app/­Contents/­MacOS/­thunderbird-bin -safe-mode" and hit return
• mark "Reset toolbars and controls"
• click "Make Changes and Restart"

alternatively re-install TB, current data will still be there

Cheers from Stockholm

We found out why Thunderbird 'stopped working' our our computers. We could send, but not receive.

We use Eset for antivirus and security app, love it. BUT the new Thunderbird triggered the program to handle SSL differently.

Here is the URL to fix the problem. https://support.eset.com/en/kb3126-disable-ssl-filtering-in-eset-windows-products

We still had to reset passwords and now Thunderbird is still acting strange, but we can receive and send email now.

Thanks for the tip! Would be interesting to know who is the bad guy: Thunderbird Mail or Eset Internet Security. In any case it's most annoying. I didn't even realize at once that there was a problem until I discovered a mismatch in the email list on my smartphone and desktop computer.