The default “remote domains” setting in Exchange 2010 allows non-delivery reports (NDRs) to be sent to all remote domains. These error message will contain internal Exchange Organization information like the server names, IP addresses, AD domain name etc.
What if you are security conscious and what to strip those information from the NDRs and yet get it sent to external senders? It is possible in Exchange 2010 SP1, with the introduction of a new parameter named “NDRDiagnosticInfoEnabled” for the Set-Domain cmdlet.
By default, the value of “NDRDiagnosticInfoEnabled” is set to $true, which means that external senders will get the full NDR.
--> The rest is on the blog : http://www.howexchangeworks.com/2011/05/stripping-internal-exchange.html