If you've already created a contact with a SMTP address then all you need to do is goto the user account in AD and select the 'Exchange General' tab. Now, select Delivery Options. Under 'forwarding address' select 'forward to', than select the 'Modify' button to search for the contact you created. Lastly, make sure you select the box that states 'Deliver messages to both forwarding address and mailbox'
-Forbsy