I did not write this filter and I am not trying to take credit for it. I am just passing on the excellent work of Gregory Sutter and Matthew Hunt.
To filter the growing SPAM plague on a UNIX system, get these files
jf-addresses(filters favorite addresses)
jf-bodychk(filters favorite messages)
jf-domains(filters favorite domains)
rc.junk(filters illegit addresses and other scary things)
rc.junk.config(configures things)
and follow the in instructions here.
Disclaimer: If your URL is listed in these files, don't waste your time emailing asking me to take it out because you swear you just purchased this URL, and did not know it was previously owned by a spammer. I know you are lying, and it's not my problem.