postfix configuration for local storage and for relay to exchange

[maurella]

Here is our tiny topology:

External world domain name:

http://www.junk.com

Internal Domain name: junk.org
Internal Linux Box name: l.junk.org
Internal Exchange Server: ms.junk.org

Routes to mailboxes:
someone@anywhere->joe@

http://www.junk.com

Router sends this through gateway to l.junk.org
If joe@

http://www.junk.com

has a mailbox on l.junk.org, then it gets stashed there. If joe@

http://www.junk.com

has a mailbox on ms.junk.org, then it gets relayed to it. Internally, messages to joe@junk.org go to the exchange server ms.junk.org.

So far, I have been able to configure postfix so that everything will either be saved on l.junk.org or relayed to ms.junk.org. Can anybody give me a clue here?

thanks in any case.

Mike