Consider the following scenario:
In Microsoft Exchange Server 2013, you create a customized delivery status notification (DSN) message by running the following New-SystemMessage cmdlet:
New-SystemMessage -DsnCode 5.7.111 -Language en -Internal $true -Text "text_from_system_message"
You create a transport rule. In the new rule, you do the following:
Set the RejectMessageReasonText value to reject messages
Add the DSN code
In this scenario, users receive an auto-reply DSN message in which the text of the RejectMessageReasonText value appears in the user section instead of the diagnostics section. Also, the customized DSN message is not displayed.
This issue occurs because the reject reason is passed as the dsnExplanation value of the SmtpResponse response. If the SmtpResponse response contains the RejectMessageReasonText value, it cannot be overridden by running the New-SystemMessage cmdlet.
To resolve this problem, install Cumulative Update 7 for Exchange Server 2013.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.