ExpiryTime Property
Returns or sets a Date indicating the date and time at which the item becomes invalid and can be deleted. Read/write.
expression.ExpiryTime
expression Required. An expression that returns a MailItem, MeetingItem, or PostItem object.
Example
This VBScript example uses the Send event and sends an item with an automatic expiration date of one week.
Function Item_Send()
Item.ExpiryTime = Date + 7
End Function