How to resolve email delivery issues due to account restrictions – MS365 Admin

Raised from ticket #2163

If a user is experiencing issues with sending emails, particularly if they receive a message indicating that the delivery has failed due to their email address not being recognized as a valid sender, follow these steps:

• Check for Account Restrictions: The user’s email account may have been blocked or flagged as spam. If we have control of the tenant, go to https://security.microsoft.com/restrictedusers to review the restrictions and follow mitigation steps before unblocking the user.
  
• Wait for Restrictions to Lift: After resolving any issues, it may take some time (up to an hour) for restrictions to be lifted. Check back after this period.
  
• Reset Their Password, Reset MFA, and Revoke All Sign in Sessions if suspicious activity is detected: If their account has been compromised or flagged, resetting their password can help. Ensure that you also set up Multi-Factor Authentication (MFA) for added security.
  
• Verify DNS Records: Ensure that tenant’s DNS records are correctly configured. This can affect email delivery.
  
• Test Sending Emails: Once the restrictions are lifted and any other necessary steps are taken, try sending an email to confirm that the issue is resolved. If problems continue, evaluate what else might be going on 🙂