In the event you find that an IP address you manage or access the Internet from is blacklisted, DNSBL can be a big help in quickly identifying who’s blacklisted you and why.
DNSBL includes links to all known public black lists and information on how to delist an IP address from each system.
Domain Name System Blacklists, also known as DNSBL’s or DNS Blacklists, are spam blocking lists that allow a website administrator to block messages from specific systems that have a history of sending spam. As their name implies, the lists are based on the Internet’s Domain Name System, which converts complicated, numerical IP address such as 184.108.40.206 into domain names like example.net, making the lists much easier to read, use, and search. If the maintainer of a DNS Blacklist has in the past received spam of any kind from a specific domain name, that server would be “blacklisted” and all messages sent from it would be either flagged or rejected from all sites that use that specific list.
For more information click here.