I am trying to add a linux firewall to a company's network
Here's my situation... Internet --> CISCO Router --> Linux Firewall --> Private LAN. On the private LAN behind the firewall, I have an exchange server. I changed the exchange server's old IP to a private IP. The linux box uses another public IP address.

I can browse the internet thru the proxy. I can send and receive email internally. I can send email to the outside world. But I cannot receive email from the outside world.

I use ipchains and ipmasqadm on the linux box that is supposed to forward email on port 25 to the private IP of the exchange server. It is a basic setup based on all the documentation I've read, but I can't get the outside email to the exchange server. Is it possible that I need to change the linux server's IP to the old public IP that the exchange server used to have? Since this is the IP that the ISP recognizes for email?

Thanks for any suggestions.

It sounds like you have a DNS problem. The linux firewall needs to have the same public IP address that is listed as your MX record. Or, simply put, if you had the exchange server working and put it behind the firewall and the firewall has a different IP address, then the mail is still looking for the old IP address. The easy way to fix that is to change the IP address of your linux box to the old IP of your exchange server as you suggested. The other way to fix it is to have the DNS records to point mail to the new IP address instead.

-Mark

Better u put some smtp proxy from opensourcefirewall.com
or TIS.

I am using sendmail as my mail relay with TIS as listner

Siddiqu.T