Multihomed Exchange Server?

Your current setup is not secure.

if you put your server on the WAN and users on the lan with the linux router, your making your server totally available to hackers. So technically they can hack all your exchange data, but your users PCs are fine.

Best solution for a small network is to put get a firewall, implement NAT, and open up port 25 for the mail server, 80 for the webserver. If you want to pop the mail server and/or use web outlook open up 110 and 80 to the mail server.

If your network if of a good size, you can get a firewall, and put the servers on the DMZ. Setup rules to allow internal and internet users access to your servers.

If you want security but don't want to get a firewall. do TCP/IP filtering on the WAN interfaces of the web server and the mail server. Only allow ports 80(web), 25(smtp), and 110(pop). to do so, go to tcp/ip properties, advanced, options tab, select tcp/ip filtering, properties, "enable tcp/ip fil....", permit only tcp ports 25, 80, 110.

Exch should be on the local lan so that the local users can connect to without sending out lan traffic out across borders.

The web server should definitely be in a DMZ allowing only port 80 from the world.

The world only needs tcp 25 to connect to the exch server.

I know I am reiterating the 1st poster, but there is additional.

Might as well take the 2nd nic out of exchange. It does more hurt then good. You would think that it would be a good idea, but exhange will become wiggy about it's connections and you will find mail not being delivered.

Like poster 1 said, you need a firewall, plain and simple. Anything that filters out traffic at this point.

So when you set up your linux router, set up IP Tables also.