MailItem.Unload Event (Outlook)
Occurs before an Outlook item is unloaded from memory, either programmatically or by user action.
This event occurs after the Close event for the Outlook item occurs, but before the Outlook item is unloaded from memory, allowing an add-in to release any resources related to the object. Although the event occurs before the Outlook item is unloaded from memory, this event cannot be canceled.
This event is meant only as a notification event, so that an add-in can dereference the object. An error occurs if any property or method for this object is called within the Unload event.