How can I stop someone from using my server to send spam?

I think my Domino server in being is used by someone to send out spam (as an open relay). Can you give me steps to follow to stop the process and any advice you think we should follow? I am new to Domino 6.
This problem is a little complex to address here. I will give you some basics.

First, you should restrict inbound relayers and outbound relayers in the configuration document to only the domains you manage. You also should set the notes.ini parameter SMTPAllHostsExternal=1. This parameter requires an OS reboot (not just a Domino restart) to take effect. There are a myriad of other settings to make your setup effective in the configuration document. Unfortunately there isn't the time or space to mention them here. I am actually writing an article on this exact topic, and it is currently coming in at about 25 pages. So, you can imagine how complex this task can be.