How can i make a Linux box act as primary MX for my domain? I am trying to setup a mail relay between the internet and my exchange server. This will handle spam and viruses. Right now I am having a hard time setting up sendmail. All help is appreciated.

I am pretty new to Linux. Is it good to use the sendmail that is installed with RH9 by default? Or is it better to uninstall the package and reconfigure it manually? I see that the sendmail server is running in services.

Here is the deal. I am looking for a internet mail gateway for my lan that will do the antispam and the antivirus. Here is my current setup

internet --- firewall --- exchange5.5 --- recipeints

I want a setup like this:

internet --- firewall --- sendmail relay --- exchange5.5 --- rececipients

First things first. Right Now my exchange5.5 server is setup as mail.dummy.org. I am very new to this. How can I point all external email to my linux box instead of the exchange 5.5 box. It looks like Sendmail is up and running. I ran netstat and I see port 25 open.

my mail.dummy.org already has a MX record out there. Its points to a public IP on my network. So do I still need to configure DNS on my linux box? How can I make sure that the mail is going to go to my linux box first before to my exchange box?