2 domains 2 exchange servers different routing?

I have an 2003 server that is running exchange 2003. I have a secondary 2003 server that is running exchange as well for availability. The problem is that all mail comes in and out of my primary server, however I need a new domain to send and receive out of the secondary server only. (will be sending a lot of email and need to make sure my primary server doesn’t get blacklisted for any reason)

Is there any way to force a certain domain to route mail to/from the secondary server?