Starting about a year or more ago, when trying to set up profiles on Thunderbird for a comcast.net email address, it would fail. The different errors generated would indicate it was a problem on the mail server, and not with thunderbird. Even comcast support couldn’t figure it out. With trial and error, I finally did. - Enter your name, address and password in the setup screens and allow it to get to the “configuration found” menu. - Select to configure manually. - Under incoming server for IMAP, Authentication Method will show 0Auth2. Change it to normal password. - For Username, it will be set to the entire email address. Remove the “@” sign and everything to the right of the “@” sign. So instead of email@domain.com it will show “email” and that’s it. - Under outgoing server for SMTP the authentication method will show 0Auth2. Change it to normal password. - If username shows the entire email address, (It shouldn’t, if you changed it for IMAP) then remove the “@” sign and everything to the right of the “@” sign. - Click the Re-Test button and it should pass. - Click the Done button and the setup should be completed with no issues. -