If you viewed the password in Saved Passwords, it indicates you're using 'normal password' authentication instead of the preferred OAuth2. First, check that cookies are enabled in TB Options/Privacy or Privacy & Security (TB 78), set the authentication to OAuth2 in Server Settings for the incoming and also in Outgoing Server (SMTP), then delete the passwords in Saved Passwords, restart TB, enter the current working account password in the OAuth browser window when prompted.

Great. Worked like a charm. Now, I'll do the same on the other 7 gmail accounts I have on TB even though they all work with their own Google "normal password" settings. I wonder why only one account I've had for years suddenly stopped working only on TB 6 days ago, but none of the others. I guess I'm changing them all to OAuth tonight. Meanwhile, I changed my overall Google password 3 times in 3 days trying to reset TB. What a pain since these changes ripple.

I worked as a consultant to Microsoft in the '90s helping develop Outlook and Extended MAPI - you'd think I would have thought about this solution, but all my other accounts in TB still are working fine with "normal password" so I never thought about the OAuth fix.

Thanks and a WELL-DESERVED thumbs-up.

I've tried so many things that it's more complicated. When my antique e-mail address - @sbcglobal.net - wouldn't work with a newer 32-bit version of Thunderbird, I found that there was an even newer (78.4.3) 64-bit version. I downloaded it and it didn't solve my problem but complicated it further. I too, get the "login failed" with both that very old e-mail address, and with a "@protonmail.com" e-mail address. I changed passwords, too. An OAuth option doesn't appear for either address. And it appears that I've destroyed my ability to review my old e-mails in Thunderbird, somehow. Can you point me in a good direction?

I'm balding more quickly than I was! Mike

I have Thunderbird running happily on a Windows 8 computer. I just got a new Windows 10 computer, installed Thunderbird, and have copied the configurations exactly the same. I have also followed the advice for a setting in Thunderbird when using on more than one computer.

I only use Thunderbird for a Gmail account, and have likewise followed the advice to allow (on google account settings) apps of lesser security. Nonetheless, while Thunderbird continues to work find on my old computer, I get this message trying to log in on the new computer: "Sending of password for user recent:[email]@gmail.com did not succeed. Mail server pop.gmail.com responded: Username and password not accepted."

This is mind boggling...

Is the authentication on the incoming servers normal password or OAuth2?

Did you enable 'recent mode' on the account?

https://support.mozilla.org/en-US/questions/1284345#answer-1305416

Thanks SF, I did those as a part of the package of trying everything from a couple hours of searches. However something curious happened, a glitch (one of a few I'm finding in my new Windows 10) which resulted in my uninstalling Thunderbird.... and then finding out that after the uninstall I need to manually remove all pieces left over in my user folder AND dump the trash. When I reinstalled all went mysteriously well, to my delight.

I'm still not through, as I figured out, to avoid a prior error, to first port over my user profile and replace the one created (not the "default" but a second one) before setting up the account. However I haven't yet gone back to set up the account settings to see if it all works. I never had such problems through a number of ports over the past 15 years (first one from Mac to Windows).