I've been a faithful Thunderbird user since the beginning - and continue to use Thunderbird with our company's Microsoft365 deployment until Monday of this week -- when suddenly I find that my credentials are being refused. The symptoms * XXX: Connected to outlook.office365.com * nothing in the activity viewer * no email coming in I've read and tried all the fixes proposed in the article at https://support.mozilla.org/en-US/kb/microsoft-oauth-authentication-and-thunderbird-202 (restarting thunderbird after each step, naturally) * have authorized Thunderbird to our Microsoft365 tenant * created and tried registering with a new thunderbird profile * have set my security settings to 'accept all cookies' * have used the config editor to remove 'oauth2.issuer' and 'oauth2.scope' values * I've checked that my account in Microsoft365 has IMAP and Authenticated SMTP enabled So, since Monday, I've been living in hell, trying to pretend that the Microsoft Outlook app for macOS is useable, but it's practically debilitating to be forced to use that piece of software. Can somebody please point me to another possible set of steps that I can use to try and diagnose this? I ''absolutely hate myself'' for having to ask for help on this, but I'm at my wit's end...