Did you switch the sign-in Audience to your AzureAD only? I had changed the audience in the app manifest; first it worked but then it failed. After switching it back, deleting the plugin and installing the plugin again i got it working. Please note, you have to delete the plugin and re-install. First I jsut installed the plugin again, that did not help.
Not sure if that was at all related and I don’t really understand the sign in audience requirement to be “signInAudience”: “AzureADandPersonalMicrosoftAccount”; but at least it works now
Which API permissions are required? I have configured all the permissions I could think of, but no success. With my user it works, but I fail to send with the user that is supposed to be used for the emails
Mail.Send
Delegated
Send mail as a user
No
Granted for XXX
Mail.Send
Application
Send mail as any user
Yes
Granted for XXX
Mail.Send.Shared
Delegated
Send mail on behalf of others