exchnage server 2k

I have an open relay in my exchange server and unfortunatly its being used to send out spam by hackers so i had to close the port in the router so now i can’t send e-mail from home using my bussiness mail.
I need help to setp up some kinda securityso I can use my e-mail system from home and block the spamers from using my server as there relay sever.

thank you