Cisco configuration IOS12.4

Hello,

I have setup a Cisco 2851 ISR with 12.4IOS installed on it. I am able to get to the internet just fine and resolve names. Everything is working great on that end. My issue is for my public DNS names on my local LAN.

For example, I am able to get to mail.mycompany.com from outside my LAN, but when I try to get to this namespace on the local LAN, it comes up with page cannot be displayed. When I go to the public IP, it does not work as well. I am able to ping this public IP and namespace. I am not sure of the commands to use in the router to set this up. Any assistance would be appreciated, as this is fustrating to my users, and I dont like giving out the private IP to them to use.

Thank you