I Can't send emails to external recipients

TA 0 Reputation points
2026-08-24T07:44:38.4+00:00

We are facing an issue in our Microsoft 365 environment where none of our users are able to send emails to external recipients outside the organization.

When a user tries to send an email externally, one of two things happens:

  • The email is delivered to the recipient's Spam/Junk folder.
  • In some cases, the sender receives an NDR/error message from Microsoft stating that the message could not be delivered because the receiving email server outside Microsoft 365 reported an error. The error also indicates "Policy violation or system error" when sending to multiple external recipients.

I have already checked our Email Authentication settings, and the domain is showing as Valid.

Exchange | Other
Exchange | Other

A powerful email and collaboration platform developed by Microsoft, designed to support enterprise-level communication and productivity. Miscellaneous topics that do not fit into specific categories.

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  1. JeseminQH 515 Reputation points Independent Advisor
    2026-08-24T09:13:52.1533333+00:00

    Hi @TA

    Regarding your issue, may I kindly ask a few questions so I can understand your issue better:  

    • Does the issue occur when sending to all external domains or only certain domains, and does it happen with a single external recipient or only with multiple recipients? If it occurs with multiple recipients, approximately how many recipients are included? 
    • When did the issue first begin, and were any changes made to DNS, SPF, DKIM, DMARC, connectors, mail flow rules, or email security settings around that time? 
    • Are users able to send and receive emails internally, and can they receive emails from external senders? 
    • Does the issue still occur when sending a plain-text email to one external recipient with no signature, links, images, or attachments? 
    • Have you run a message trace for an affected email? If so, could you share a screenshot showing the trace result and the recipient server’s response? For more details, please refer to: Trace an email message in Exchange Online
    • Could you also provide a screenshot of the error or NDR received when sending the email? Please hide personal or sensitive information but leave the complete error code and server response visible. 

    Hope to hear back from you soon. 

    Note: Please follow the steps in the forum documentation to enable e-mail notifications if you want to receive the related email notification for this thread. 

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