Inconsistent NDR Messages with Transport Rule for Domain Redirection

Question

Hi,

I am experiencing an issue with a transport rule I have set up in my Microsoft 365 tenant. The rule is intended to block emails sent to the domain abc.com and provide senders with a Non-Delivery Report (NDR) explaining that the domain has changed and to email us at xyz.com instead. 

However, during testing, I’ve noticed inconsistent behavior:

• Some senders receive the correct explanation as intended.
• Others receive the NDR message as an attachment.
• A few receive a different kind of NDR that mentions the transport rule rejected the message.

This inconsistency is causing confusion among our contacts, and I would appreciate your assistance in resolving this matter so that all senders receive the correct NDR message as configured.

Thank you for your attention to this matter.

Best Regards, Janak Khadka

Answer 1

Hi @JanakKhadka，

Welcome to the Microsoft Technical Support Forum.

 

According to your description, senders who sent mail to the domain abc.com received different types of NDRs.

 

For this question, I would like to explain that Exchange NDRs are designed to be easy for email users and administrators to read and understand. There are two different formats for NDRs. The latest style NDR includes a description of the problem written in common language and repair steps. The following figure shows the format of such an NDR:

The information provided in the latest style NDR is designed to help a typical email user solve the problem immediately. If this is not possible, the NDR provides more information for administrators and links that can be used to get more help on the Web.

For NDRs that do not have the latest format, the information may be divided into two parts: user information and administrator diagnostic information. The following figure shows the format of one type of Exchange Online NDR:

So the problem you are experiencing is normal, there doesn't look to be a problem with your setup, and it is expected that the sender receives an NDR in a different format.

Refer to: Email non-delivery report (NDR) and SMTP errors in Exchange Online - Exchange | Microsoft Learn

Please feel free to contact me if you have any queries.

Best,

Jake Zhang