Use the Delivery Restrictions property page to accept or reject messages from any sender listed in the Microsoft Exchange Server directory. For example, if a message is addressed to cc:Mail users, it is returned to the sender if the sender's address is in the Reject messages from box or does not appear in the Accept messages from box. Delivery restrictions do not affect incoming messages. The default is to accept messages from all senders and reject messages from none.
For more information about using delivery restrictions, see Microsoft Exchange Server Getting Started.