Enhanced NDRs now available in Exchange Online

Although still listed as “In Development“, the Enhanced non-delivery reports (NDRs) are now available in Exchange Online.

The Enhanced NDR present a great improvement to both end users and Office 365 administrators. The new NDRs are intended to make it easier for the end-user to understand why their message was not delivered, and the added in-depth information enables Office 365 administrator to faster perform troubleshooting and quickly resolve message delivery problems, so the business information flow and collaboration can get back on track.

So far, when Exchange Online could not process a mail, a Delivery Status Notifications (DSNs) was returned to the message sender with NDR information. This DSN message contained a top section with basic error description and a DSN code reference to what has caused the mail flow error. The lower section of the DSN, called Diagnostic information for administrators, included the SMTP message header information, listed in six sections;

Generating server – Name of the SMTP mail server that created the NDR
Rejected recipient – Email addresses of each of the recipients
Remote server – Name of the mail server that rejected the message.
Enhanced status code – DSN status code, in the format ### x.y.z, as defined in RFC 3463. This value is assigned by the mail server that have failed to deliver the message.
SMTP response – explanation of the DNS status code. This is returned by the mail server that rejected the original message.
Original message headers – Message header fields of the rejected message, which can provide diagnostic information, including SPF authentication, mail path, anti spam details, and much more.

NDR Legacy

This has all changed and is now simplified with the Enhanced NDRs, which in a more end-user friendly manner explains why the mail has not been delivered and how the issue can be resolved and who needs to fix it (sender side, recipient side, or Microsoft Support).

The Enhanced NDRs are devided in three sections;

  • Graphic summery  – Error and cause description, and a “Fix-it Owner Indicator” showing with red where in the mail handling process the error must be resolved.
    The Office 365 logo is displayed when Office 365 is generating the NDR and either sender or recipient is hosted in Office 365.


  • How to Fix it” – Contains supplement error description and suggested solution steps for the end-user, who received the NDR. In case the issue can’t be resolved by the end-user, Office 365 suggests the resolution and provides information about who the end-user needs to contact and what should be communicated.


  • More Info for Email Admins” – Detailed error description and in-depth explanation of how to resolve the issue.
    This section also includes the following subsections Original Message details, Error Details, Message Hops, and Original Message Headers.The Office 365 administrator still has access to verbose message details, as the Error Details subsection includes the former described DSN status code, and the Original Message Headers subsection includes the complete message header fields of the rejected message, which can be used for further diagnostic information.


Note, that Office 365 may still generate standard NDRs in some cased, as the new feature is being rolled out across the Exchange Online service. But most of the NDRs generated by Office 365 should be processed in the new enhanced format.

Additional information:

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