A lot of people lately have been asking me what steps they should take to resolve their spam problems. Two client-side programs come to mind:
These do a great job of stopping mail because people become part of a community.
Your large ISPs now offer a similiar service if they have a "report spam" button. Ultimately, people are, on average, a good read about what is spam, and what is not. Some major ISPs, such as hotmail.com, aol.com, earthlink.net, and yahoo.com have these features built-in.