Recipient Address rewriting and Transport

[Rosenbaum, Larry M.]

I would like to do the following:  If the recipient is 
u...@mail.example.com<mailto:u...@mail.example.com>, rewrite the address to 
u...@example.com<mailto:u...@example.com> and relay it to server 
exch.example.com. How would we do this?

We are running Postfix 3.0.2 on RHEL6.

Thanks,
Larry