hi acdc, sorry about he delay in replying

Most spam mail just 'spoof' your address and don't actually use any of your bandwidth.

Ok, here is what I've done so far:
registered a domain for my website
setup server 2003 to host my website
setup a pop3 and smtp server in server 03 so I can have email addresses for my website. I used mostly default settings except where I had to change ip address/domain settings. I have authentication on incoming and outgoing messages.
A few days after I set this up I got an email from my isp saying that they have temporarily disabled my account because of spam coming from my ip address, that's when I noticed all the spam that my avast mail scanner was scanning. Just random IP's were sending mail. So I need to know how to stop this so my isp doesn't shut me off again. Thanks

I'd suggest by scanning and removing all spyware/viruses off your network, and then impliment some sort of anti-spam software as mentioned earlier.

Unfortunately there isn't alot else that can be done