The Spamhaus PBL, a one year old anti-spam heavyweight

One-year retrospective on Spamhaus's Policy Block List (PBL): the article explains PBL's role in listing end-user IP ranges that should not send unauthenticated email, how it complements the SBL/XBL and ZEN services, the two listing categories (Spamhaus-maintained and ISP-supplied), the option for ISPs to maintain their own ranges (covering about 25% / ~100 million IPs), and claimed spam reduction benefits (stopping 80–90% at the front door and up to ~99.6% when combined with other techniques); it encourages ISPs and end-users to adopt PBL/Zen to reduce spam.