Spam Prevention Early Warning System

The Spam Prevention Early Warning System (SPEWS) was an anonymous, volunteer-operated service that maintained a list of IP address ranges belonging to internet service providers (ISPs) that hosted spammers, were considered spam-friendly, or hosted websites advertised in spam. Internet sites could query the list and use it as an additional source of information when deciding whether to block or filter incoming email.

Unlike blocklists that targeted only individual offending addresses, SPEWS deliberately listed wide blocks of address space around a spam source. This caused "collateral" blocking of unrelated customers and was intended to pressure ISPs into removing spammers from their networks. The combination of that tactic, the anonymity of its operators, and the absence of any way to appeal a listing made the service both influential and contentious. A Florida attorney who sued its operators called them "vigilantes of the Internet".

For a time, the list was distributed through Joe Jared's Osirusoft service. In August 2003, after months of distributed denial-of-service (DDoS) attacks, Jared closed Osirusoft, although mirror sites kept SPEWS available. The SPEWS database was last updated on 24 August 2006, after which the resource dnsbl.com listed its status as dead. It was succeeded by the service called the Anonymous Postmaster Early Warning System (APEWS) in January 2007.