For Gmail, you can use https://github.com/google/gmail-oauth2-tools/tree/master/go/....

Generating app passwords for those would work.

Yeah, I use an app specific password with Gmail, like the setup suggested by https://git-send-email.io/#step-2

Exchange historically had a tendency to mangle emails sent through it (whitespace changes, line wrap, etc), which is obviously bad news for patchmails. I dunno if it's any better these days.

I use msmtp with a tool from the oauth2-tools repo to do the rotation token dance. Need to register your own app with Google though.

davmail supports smtp through outlook(365)

Yeah, I used DAVMail with Emacs+MSMTP+MPOP+notmuch for ages. Works really well, the only occasional thing I had to do was reauthenticate the token, which pops up in a browser window.

I think you could set up postfix to smtp forward to those services. So it could handle the oauth2 and you wouldn’t need to configure your client

I use an app password but https://github.com/AdityaGarg8/git-credential-email apparently supports OAuth with Gmail, yahoo and outlook

I tried this with Gmail and Outlook. Works flawlessly and also doesn't need to authenticate frequently. The Authen::SASL thing was a catch though.

git-send-email also has some quirks for Outlook which have been recently merged.