Gets the message's expiration time.
When a message is sent, the Expiration header field is left unassigned. After the send method completes, the Expiration header holds the expiration time of the message.
This property is read-only because the expiration time of a message is set by adding the time-to-live argument of QAManagerBaseputMessageTimeToLive to the current time.
The expiration time is in units that are natural for the platform. For Windows/PocketPC platforms, expiration is a SYSTEMTIME, converted to a FILETIME, which is copied to an qa_long value.
For more information about getting and setting message headers and properties, see Message headers and message properties.
The expiration time.