exchange server problem

I am a complete novice when it comes to exchange. I am helping with a relocation of office facility. They are running NT4.0 SP6 with echange server 5.5. When we moved the servers we now have a different IP & DNS address from the ISP.When we were not able to send or recieve email, I started exchange, opened Configuation/connections and changed the "forward all mail to host" IP address to the new DNS ip given to me by the ISP. It still is not sending or recieving. It was functioning properly at the old location with the DNS as the forwarding address. Please if anyone can help, I would appreciate it as I have users breathing down my neck...