DNS Records

I have a simple question. I am setting up a new exchange server
for my office. I bought a domain name and is registered. I have a
Road runner circuit with a Public Static IP. I am going to install
the exchange server on my internal network with a private IP and
will port forward 25 from my firewall/router to this server. My
question is what DNS entries I need to make with my ISP so i can
get all SMTP mail. I am naming my exchange server as
SERVER1.mydomain.com. Somewhere I read that U need to
create entries or records with name as MAIL and somewhere
they say it should have your server name,,So I am a bit confused.
Can someone tell me and also tell me if i missed something in
here
THanks