The DSNNotify property specifies whether or not the message should be included in any failed DSN issued for this message transmission.
Sets or returns a String value.
The DSNNotify property may be set with on of the following keywords:
NEVER requests that a DSN not be returned to the sender under any conditions
SUCCESS requests that a DSN be issued on successful delivery.
FAILURE requests that a DSN be issued on delivery failure.
DELAY requests that a DSN be issued if the message has been delayed for an unusual amount
of time.
Multiple keywords, separated by commas, may be set; however, the NEVER keyword MUST appear by
itself.
DSN stands for "Delivery Status Notifications", it is an ESMTP
extension that is implemented by most modern mail servers.
See RFC1891
for details.