I have several G-Suite accounts all handled by Google. imap.gmail.com and smtp.gmail.com, OAuth2 . They all work ... except for one I know that I have the password correct for readers@slowlyboiledfrog.com. It has been working just fine on another computer (which was stolen the other day along with the USB drive containing the backup). Using that password and any browser, I can log in to that account or to gmail with that account. However, every time I try to set it up in Thunderbird I get an "Unable to log in at server. Probably wrong configuration, username or password " message. The configuration is identical to other accounts with the same domain. The password is verified. The username is verified two ways: Through the Google account and gmail. I tried turning on "allow less secure apps." No difference and it is not turned on with any of the other accounts from the same domain. IT'S DRIVING ME NUTS. I am not terribly rational to begin with.