Custom messages in NDRs are replaced by default system messages in Microsoft 365

Original KB number:   3044155

Problem

You set a transport rule in Microsoft 365 to return a non-delivery report (NDR) that displays a custom message. However, the custom message in the NDR is overwritten by the standard NDR message. This issue occurs in either of the following situations:

• The sender and recipient belong to different Microsoft 365 organizations.
• The sender has a Microsoft 365 mailbox, and the recipient belongs to an external Exchange Server organization.

Cause

The DSNConversionMode parameter isn't set to PreserveDSNBody.

Solution

Use the Set-TransportConfig cmdlet to set the DSNConversionMode parameter to the value of PreserveDSNBody. This transport configuration setting must be changed at the organization that receives the NDR.

To do this, follow these steps:

1. Connect to Exchange Online by using the Remote Desktop Services module for Windows PowerShell. For more info about how to do this, see Connect to Exchange Online PowerShell.

2. Run the following command:

   Set-TransportConfig -DSNConversionMode PreserveDSNBody
   

More information

The DSNConversionMode parameter determines the format to use for delivery status notifications (DSNs). The parameter can be set to one of the following values:

• UseExchangeDSNs

  Exchange converts the DSNs to the Exchange Server 2013 DSN format. This format is the same as the Exchange Server 2010 DSN format. However, any customized text or attachments that were associated with the original DSN are overwritten if the DSN is delivered from another Microsoft 365 organization or from an external organization.

• PreserveDSNBody

  Exchange converts the DSNs to the Exchange Server 2013 DSN format, and the text in the body of the DSN message is retained.

• DoNotConvert

  Exchange does not modify the DSN message. Instead, Exchange delivers the message as a standard message.

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