The Spamhaus Policy Blocklist (PBL) is a DNS-based blocklist (DNSBL) dataset containing end-user IP address ranges from which email should not be sent directly to a final mail destination. It is predominantly IPv4-based but also includes IPv6 ranges, listed in CIDR format. The PBL identifies end-user IP address ranges that should not be attempting to directly deliver unauthenticated SMTP email to any Internet mail server. IPs listed in the PBL are expected to submit email — using authentication — to an SMTP relay server rather than delivering directly to destination MX servers. The dataset covers both dynamic and static IPs that, by policy (either the block owner's or Spamhaus' interim policy), should not be sending email directly to third-party MX servers. It contains more than 1.4 billion IPv4 addresses, covering approximately 40% of routable IPv4 space. Networks and ISPs contribute directly to the dataset by submitting and maintaining their own IP ranges. Spamhaus supplements this with its own research, identifying end-user IP space with high concentrations of botnet-compromised hosts ("botnet zombies") that are a source of spam. The PBL is designed to be queried exclusively at the SMTP connection stage — against the connecting IP — not during content filtering. It is available free of charge for low-volume, non-commercial use via a real-time DNS query service. Commercial use requires an annual subscription. Network owners and ISPs can manage their ranges via the PBL ISP portal, setting inclusion/exclusion policies. End users whose IPs are listed can request removal via the Spamhaus Reputation Checker.