In Exchange 2007 and above, it is possible to customize the bounceback messages Exchange sends for undeliverables, including adding telephone numbers, URLs, et cetera.
To get current customized messages:
Get-SystemMessage
To get the full set of originals:
Get-SystemMessage –Original > c:\original_ndrs.txt
To set a new one:
New-SystemMessage -DsnCode 5.7.1 -Internal:$True -Language en -Text "Sorry, the email could not be delivered..."
Note the DSN code; there are many, and you will need to set the one(s) whose NDR you want to change. Some HTML is permitted.
Much more detail is here: