DSN (delivery status notification)

Notification that reports the result of an attempt to deliver an e-mail message. DSNs are designed so they can be read by humans or computers. A DSN is made up of the DSN code and the DSN message. The DSN code is a three-digit string of numbers, such as 5.1.2., that indicates the status of the message. The DSN message is the text that explains the status and may recommend user action. [Exchange 2007]