My friend was unable to configure his outlook.com email address in Thunderbird (143.0.1) while I had no problem doing so in mine (140.3.0esr). We both had installed other email addresses already configured with no problem. I upgraded my second laptop from the esr version to his recommended release version, and hey presto, I suffered the same fate. This is definitely a bug within Thunderbird 143.0.1 which is the current release version. I had not previously added the outlook email to Tbird as it is not my main email address. More info: The error message encountered was: Authentication failed: Please check the username and password When you click on the "More information" link, it says: "Exchange auth error" Please note that we checked the username and password and verified them as correct. I addition, I was successful using that username/password on the 140 esr version and it worked perfectly.