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Microsoft 365 SMTP server intermittently rejecting connections

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 SMT… (read more)

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.

Asked by lesrose1959 5 months ago

Answered by gp 2 months ago