Spam relies on volume. Slowlists thwrart that. If you throttle spam you can kill it, because spam's only selling point is high volume at high speed. The goal of slowlists is the complete elimination of spam from irresponsible ISPs by reducing it to an unprofitable level. It does not directly address spam orginating from rogue users of otherwise good ISPs.

Slowlists restrict a sender's volume of email by delaying the receiver's response according to the reputation of (the IP address of) the sender. Senders in good grace move email without penalty; unknown senders are slowed, to provide a window to verify their volume; probable spammers are asked to retry later, to show their pennance. This last delay can be calibrated to squelch even the huge number of open proxies. No email is ever rejected: only the patience of the sender is tried.

A sender's good reputation is shared with other good senders, to create a society of legitimate email movers. To be effective, a slowlists society should be large and communicate as if they were a single receiver, to throttle volume to any part of the society. Outsiders can still send mail -- slowly -- and over time gain the legitimacy they deserve.

Slowlists also use delay to distinguish legitimate senders from spammers. Legitimate senders will cope with the initial delay until their reputation earns them faster handling. For a spammer who rushes the delay provides time for their tarnished reputation to spread.

There are many definitions of spam, but we stand by this one: a volume of email sent in excess of the sender's good reputation. Slowlists attack spam at this very definition: limit the volume of email received from unknown senders or senders in disrepute.

© 2003 Bryan Costales and Perforce, Inc. All rights reserved.