The Spamhaus Project (aka Spamhaus Black List) is one of the world's preeminent anti-spam organizations. Spamhaus fights spam by tracking spam activity via its own network of sensors and data sources and then compiling lists of Internet Protocol addresses associated with spam activity. These IP addresses are added to the Spamhaus Blocklist ("SBL"), which is widely used by ISPs around the world. ISPs use the SBL, along with other data, to determine which IP ranges to block from their network.
At the time an IP address is added to the SBL, Spamhaus generates and transmits an abuse complaint to the network responsible for the cited IP address. If the network responsible for the IP address takes action to remove the offending content hosted at the cited IP address, Spamhaus will remove the IP address from the SBL. In virtually every case, ISPs would respond to Spamhaus abuse complaints and take action to remove the spam-related content from their network.