Active Directory User account forwarding email to external account

We have a user who for various reasons is not a member of our domain.  He has his own email account hosted off site, and is not affiliated with our exchange server at all.  I currently have a contact record for him in active directory, which forwards all internal mail to his own outside email.  However, some complains have been coming in from customers who simply try to send him emails and they assume his email address is the same as the rest of our employees (first.last@ourdomain.com).  Well, they can't send him email this way as he doesn't have an address like the rest of us.  If I delete his contact record and just give him a regular user account and mailbox in AD and exchange, could I just have any mail forwarded to this new address/account sent on to his external account?