Dynamics Community Forum Thread Details

Exchange Online → Mail flow / SMTP

Hello Dynamics 365 BC Community

After following Microsoft's official documentation step-by-step to configure SMTP AUTH with OAuth 2.0 Client Credentials Flow (Application permissions) for sending emails from a third-party application (Microsoft Dynamics 365 Business Central),

authentication fails with 535 5.7.3 Authentication unsuccessful even though all prerequisites are confirmed in place:

•   Token is successfully issued by Microsoft Entra ID with the correct scope
•   All required permissions are granted with admin consent
•   Service Principal exists in Exchange Online with correct role assignments
•   Test-ServicePrincipalAuthorization returns InScope: True for the target mailbox
•   SMTP AUTH is enabled at the mailbox level
•   More than 44 hours have elapsed since the last configuration change (replication should be complete)