I get the attached popup: Authentication failure while connecting to server imap.googlemail.com. My account is set up like follows: account3 (imap) imap.googlemail.com:993 SSL/TLS OAuth2 smtp.googlemail.com:465 SSL/TLS OAuth2 true Problem started when I had "Less secure App Access" turned on. I then turned it off and on again. The problem has persisted throughout. I had 2FA turned on when the problem started. Thunderbird would take me through the full login and succeed, but give the same error. I've turned it off and the problem persists. I've tried clearing Thunderbird's password cache and restarting the machine but that didn't fix it either. Meanwhile I can log in to the account from other platforms (gmail web, gmail android, pidgin desktop) using the same password. How can I log in to my gmail account again? This is the first time I've encountered a problem like this in Thunderbird, so I'm not familiar with all the debugging tools. Just let me know how to access logs/debug and I'll post anything that can help. Thanks!