technique in the SpamWars
defining a list of senders in your EMail client who you agree to get email from
none of their messages ever get marked as Spam by your filter
maybe it's really hard for anyone not on your White List to even get a message to you (Earth Link's non-default setting works this way, sending a bounce to the sender making them come online to fill out a form with a Captcha to get approved).
related: Buddy List