[TriLUG] mail relaying

[trilug@trilug.org]

At last count between myself and my wife we download mail from roughly seven pop accounts.  Since connecting to Roadrunner I can no longer send all my mail, regardless of the return address, through my old mindspring SMTP outgoing mail server and Roadrunner won't forward mail from e-mail addresses other than xx.rr.com.  

From everything I've read setting up a firewall to forward mail is A Very Bad Thing mostly because of fears of people using your SMTP mail server for mail spamming.

I am running Red Hat 7.1 on my current firewall.  I have two ethernet cards: eth0 and eth1.  Is there a way to set up my server to forward mail that arrives only on eth1 (inside link) while blocking all forwarding requests coming from eth0?

I've read some of the man pages and looked through my "Linux Bible" book but I can't find any instructions on how to set this up - just information on why I shouldn't do this.

Any thoughts, pointers, or suggestions?

Any help would be greatly appreciated.

Thanks!

Greg