Ok, I'm going to try to explain this as best as I can while hopefully not losing anyone.

Currently we have an intranet that has a server that is running:
Postfix (primary email server)
Router (gateway to internet)

The postfix server has been the primary email server for some time now and IS working normal. We are switching to an exchange 2003 email server.

So lets say a normal users email is user@work.com. The ISP's DNS MX record for @work.com points to server.work.com which is actually the physical postfix server, which the hostname is server and the FQDN for the intranet is server.intranet.internalwork.net, IP address is So right now as said, users that are created unix accounts on server can send and receive email fine, both to other postfix accounts and external email.

Ok, so now we have a 2003 exchange server added to the same subnet. Name of the exchange server will be exchange and the IP is and the FQDN is exchange.intranet.internalwork.net. The exchange server is soon going to be the primary mail server, but for right now we HAVE to have both the postfix server and the exchange server running. The exchange server also is running AD and a secondary DNS for now. I setup a test account named test@work.com. Ok, on exchange with the test account, I can send out email to other users on exchange, and I can ONLY send out emails outside of work.com. Meaning I can send email to yahoo.com, gmail.com, hotmail.com, ect... But I CANNOT send email to any user currently on the postfix server at the @work.com domain. I don't get any bounce messages, and I don't get any errors. The postfix server doesn't receive any errors, and does not get the email message at all.

Now on the postfix server, when user@work.com tries to send an email to test@work.com it gets a bounce message saying unknown user: "test"

I have tried adding the test user to /etc/postfix/virtual and to /etc/aliases but nothing is working.

I am not sure if this is a DNS issue or a postfix issue.

Basically to wrap this up, postfix server can't send to the exchange server on the same subnet but works with everything else, exchange server can't receive email from anything outside of itself (everything routes through the postfix server though), and the exchange server can't send only to the postfix server but can send email to outside domains.

Any hints, clues, ideas, directions, howtos, or anything would be helpful at this moment. Maybe I am missing something on the DNS in both domains, or the ISP has to add an extra MX record, or postfix is missing something.

IDK, I'll find a way to buy a beer to someone if they can figure this out.