Are you using pop.mail.yahoo.com on port 995 and smtp.mail.yahoo.com on port 465; SSL/TLS, OAuth2, User name = email address? Did you remove passwords from Saved Passwords, then restart TB? Is your TB up to date, at least 68 or 78? Is POP enabled in Yahoo webmail?

I am actually a paying Yahoo customer (maybe not much longer) so it's plus.pop.mail.yahoo.com Yes to ports, SSL/TLS, OAuth2, User name = email address. I do not have any saved passwords. I've restarted TB several times today to no effect. TB is the latest version. I cleared all cookies just in case.

Is POP enabled in Yahoo webmail? I think so--I've been using it for years. I'm not even sure where to look for that on Yahoo.

I am using a PC running Windows 10 BTW.

Is there a magic answer now?  ;-)

I haven't encountered authentication issues with Plus accounts. If your TB is up to date, it's possible, but unlikely, that the plus.* servers aren't configured for OAuth2, like the free servers, or that TB does not support OAuth2 for the plus.* servers. In the meantime, you may have to use 'normal password' authentication but use an app password in place of the regular account password.

https://help.yahoo.com/kb/generate-third-party-passwords-sln15241.html

Hmmm, I did look at that third party password page yesterday, but I didn't know where to enter the password that was generated. I am not getting any log in box when TB starts up, just that error msg.

Oh! So I change the authentication method to "Normal Password" in the TB settings? Then I get a chance to log in? I'll try it.

THanks.

It worked! So I guess my next step is to complain to Yahoo so I don't have to generate passwords all the time. Or stay logged in forever...

Thank you!

The password is stored in Saved Passwords if the relevant box is checked in the password prompt window. If that box is missing, see these instructions:

http://kb.mozillazine.org/Password_not_remembered_-_Thunderbird