The observant among you may have noticed that starting in Exchange 2007 Service Pack 1, Rollup 4, a new parameter debuted for Set-TransportConfig: DSNConversionMode. Those of you who like to experiment have probably already derived what it is that this does.
The Delivery Service Notification, or DSN, is an ever present harbinger of problems. They crop up for a number of user, network, and occasionally server induced problems. They are your mail server's way of saying "I think something went wrong." The problem with DSNs is that they are generated by your mail server, and your mail server (unlike many humans) speaks raw SMTP. SMTP is completely readable in the same way that teenagers texting each other are completely readable. To the uninitiated, it looks a lot like garbage.