spam, what to do:)

My question is this. The company I work for has a no spam policy. Sometimes users do and of course we shut them off. My own feelings asside its what is considered proper in the isp community so we do it with out question. However, what is the best policy and procedure to prevent people from spamming in the first place and secondly if they do and get terminated fix the damage done. I have no desire to support spam or enable spammers but there are bad users and sometimes they do. Any positive advise on dealing with these guys above just turning them off would be helpful.