A blackhole list, sometimes simply referred to as a blacklist, is the publication of a group of ISP addresses known to be sources of spam, a type of e-mail more formally known as unsolicited commercial e-mail (UCE). The goal of a blackhole list is to provide a list of IP addresses that a network can use to filter out undesireable traffic. After filtering, traffic coming or going to an IP address on the list simply disappears, as if it were swallowed by an astronomical black hole. The Mail Abuse Prevention System (MAPS) Real-time Blackhole List (RBL), which has over 3000 entries, is one of the most popular blackhole lists. Begun as a personal project by Paul Vixie, it used by hundreds of servers around the world. Other popular blackhole lists include the Relay Spam Stopper and the Dialup User List.