Is the app only authentication for unattended daemon/service apps still not supported by Microsoft 365? Is there any Timeline for this ?
As far as we know, app-only OAUTH2 authentication for SMTP is still not supported by Microsoft 365. We are not aware of any timelines for this - you will have to ask Microsoft to learn more.
However, Microsoft 365 still supports password-based authentication for SMTP, and it's also possible to send e-mail via EWS, which does support app-only OAUTH2 authentication for unattended applications.
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