In a Microsoft Exchange Server 2007 environment, you create a transport rule that operates under the "when the Content-Type contains report-type=disposition-notification" condition. However, the transport rule is not applied to Message Delivery Notifications (MDNs).
Exchange Server 2007 checks only the value of the "Content-Type" parameter of the MIME header. Exchange Server 2007 does not check the value of the "report-type=disposition-notification" parameter of the MIME header.
For example, a typical MDN MIME header resembles the following: