Several organizations publish e-mail (or any other service) abuse lists (aka RBL, abbreviation for "Real-time Blackhole List") using DNS (Domain Names System) protocol, concepts and software (DNSBL black lists). This script inquires those lists to determine if a particular host is present. Inclusion of a particular list in this utility should not be construed as an endorsement by the script author. I use some of these lists for email filtering. I believe some of these lists are evil. You should visit their web pages, read their policies, and decide for yourself. This free dnsstuff tool supports both traditional DNSBL (IP address) and RHSBL (domain name).