Thunderbird-Hilfeforum

I've been running Tbird on Windows for many years. About 2 weeks ago something changed, either in Tbird or at Microsoft, which stops me from sending to the Office 365 SMTP server. I can send and receive using Outlook on the Office website, but I can't send locally from Tbird. Error message screenshot herewith. I have tried every possible permutation of server settings, which currently are:

Server name: smtp.office365.com Port: 587 Security: START/TLS Authentication: OAuth2

MS support says these are correct, and they are at wits' end to understand what is going on. They asked me to ask Tbird support, so I am.

I should add that at about the same time I started getting SMTP rejections in Gmail on my Android phone, and miraculously that was corrected yesterday, without any action from me. There is something odd going on at Microsoft - does anyone know what it is? My other accounts on Tbird work fine of course.

New Thunderbird Version 115.0 Every time Thunderbird checks for new messages, there is a popup relating to "login to my hotmail account". There is no prompt for an actual password as it is saved in the profile settings. The popup stays on screen for 3 seconds and is very annoying. This never happened with any of the previous versions. It also happens when I click "Get Messages", and it doesn't matter which one of my many inboxes has the focus. Image attached.