Repeated "Authentication Failure" trying to connect to outlook.live.com servers using IMAP.

Using the settings downloaded by Thunderbird. https://autoconfig.thunderbird.net/v1.1/hotmail.com They are correct, and include oauth for SMTP. So if you are modifying them it is probably the issue, if you are using anything earlier that the current ESR branch of Thunderbird then connection failures for Microsoft sites is more than probable. The current release of Thunderbird does not use IMAP or SMTP when connecting to Hotmail/office365 it uses the Microsoft Graph framework The next the most common cause of account setup failure lives in the antivirus products installed in addition to Windows defender. * The download of settings does not complete because the antivirus product blocks Thunderbird accessing the internet (firewall component) * The connection does not verify (because antivirus is trying to scan a connection that has no emails. Ooops) * The dialog to authenticate does not open in the web browser. Problems with passing links via the operating system Look at the anti phishing tools your antivirus installed. * You account approval from the browser does not update into Thunderbird. Multiple common issues here; # The antivirus is blocking the Local-host adapter. # There is another program on the system that is consuming data on that adapter (usually a development environment or web server product, Apache et. al.) # You have cookies disabled in Thunderbird or the web browser. (Enable cookies) Then you have the "other" issues caused by the tenants in business solutions (not all office365 is the same) choices as to what software can access their exchange and if they are going to support SMTP and IMAP/POP. Some business users are restricted to only use Microsoft Outlook for instance. This is an exceedingly complex area made that way by Microsoft. Now the expectations of Microsoft as to how you may connect to their services has changed significantly since Thunderbird 115 was released. But there is a support article on that, have you read it? https://support.mozilla.org/en-US/kb/microsoft-oauth-authentication-and-thunderbird-202 Fundamentally I would not expect Thunderbird 115 to connect to Hotmail using oauth at all successfully. There have been many Microsoft specific changes since the 2023 release of version 115.