> man procmailrc?

 The problem is, that procmail only protects you, not the list nor other
users on your host.

 I like the idea which I have seen on my provider's list: A wrapper around
sendmail which is able to protect you with one or two rules w/o the need
to programm sendmail with its small abilities.

 More: http://www.obtuse.com/ follow smtpd.

-- 
Markus Illenseer