What is Spamhaus?

Spamhaus is a nonprofit organization founded in 1998 by Steve Linford. It provides threat intelligence and real-time blocklists (DNSBLs) that identify IP addresses and domains associated with spam, phishing, malware, and other abusive email practices. Its blocklists are among the most widely deployed in the email industry, consulted by the majority of mail servers and email security gateways worldwide.

The core of Spamhaus's operation is its suite of Domain Name System-based Blackhole Lists (DNSBLs). The most famous is the Spamhaus Block List (SBL), which lists IP addresses known to send spam or host spam operations. Other lists include the Exploits Block List (XBL), covering hijacked PCs and compromised servers, and the Policy Block List (PBL), which lists IP address ranges that should never send unauthenticated email. Mail administrators configure their MTAs to query these DNSBLs in real time; a positive match causes the message to be rejected, flagged, or quarantined. Spamhaus also maintains the Domain Block List (DBL) for domains used in spam, and the ZEN list, which combines SBL, XBL, and PBL into a single query.

Spamhaus operates from a position of authority in the email ecosystem. Its data is aggregated from a global network of honeypots, spam traps, and user reports, and is curated by a team of analysts. While some critics have raised concerns about false positives or lack of due process, Spamhaus remains a cornerstone of email anti-abuse infrastructure. Its lists are free for noncommercial use and licensed to large providers and security vendors. The organization also publishes threat intelligence reports and operates the Spamhaus Project website, which provides lookup tools and educational resources.