Update: The full timeline for retirement of Basic Authentication in Exchange Online is now published in Basic Authentication Deprecation in Exchange Online – September 2022 Update.
It’s been a few ...
Updated Sep 01, 2022
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ZoltanLehoczky as far as I know thunderbird will need to be patched to support OAuth for Azure AD.
The dark side of oauth is that every provider needs special support in the client. At least to learn the provider endpoint URLs, and in the case of Azure AD, to do the specific things that are different from Google related to refresh cookies and public clients (eg PCKE).
So, until Thunderbird is patched to support O365 it won't work. Hopefully once MS provides the developer documentation someone will start on that. It is also a little unclear to me how Mozilla will get itself a client id.
It is very hard to see how the October deadline is feasible at this point, when it is now March and there is no developer documentation, and no date for SMTP roll out, and not even a prototype patch to make Thunderbird work.