The Subscribed property is used to determine if the current
mailbox has been subscribed to by the user. If the property returns
False, the server has indicated that the user has not subscribed to
the mailbox. If the property returns True, the current mailbox is in
the user's subscription list.
Setting the Subscribed property changes the subscription
status of the current mailbox. Setting the property to True adds the
mailbox to the user's list of subscribed mailboxes, while setting it
to False removes the mailbox from the subscription list.