I have a Postfix server running on Mandrake 9.1. My main e-mail server for my domain is Exchange 2000. The Postfix server is a Webserver and Sympa Listserver. All e-mail accounts with addresses like user@domain.dom are on the Exchange server. The Postfix server has addresses that look like user@listserv.domain.dom. The Postfix server recieves messages on my network from accounts on the Exchange server no problem. When the Postfix server sends a message addressed to the Exchange server (user@domain.dom), it changes the address to user@listserv.domain.dom, and so are recieved locally.