A Domain Name System List, also known as a DNSL, is a list of IP numbers that can be queried using the DNS protocol

DNS Blacklist or DNS Block Lists (DNSBL, RBL) are usually spam blocking lists that allow an email server administrator and Internet Service Providers (ISP) to block emails from specific IP addresses that are sending spam or have been security compromised.

DNS lists are also used to list Scam, Phish, Virus, Bots and multiple other type of lists. DNS lists can also be white lists (DNSWL), and is sometimes used by proxy web servers to allow children, students, employees or other groups only specific and controlled web or Internet access.

If the maintainer of a DNS Blacklist has received confirmed information of spam abuse originating from a specific IP address, and the spam abuse complies with the list listing policies, that administrator may add the IP number to the black list. The practical effect would be that the server would be “blacklisted” and all messages received from that server would either be flagged or rejected from all sites that use that specific list.

The original use of a DNSBL was to block spam. Most modern mail server software have support for DNSBL and mail server administrators can easily manage which block lists they wish to use for their clients. Companies like DumpSpam.com also offer to create blacklists specifically for administration by anyone. The DumpSpam DNSBL systems can be integrated and connected, in a neural type network, where each system is a node on a central or multiple central systems similar to a multi dimensional mesh or layered grid.

Generally DNSBL systems do not read or concern themselves with the content of emails only the sender IP address is relevant and user privacy is therefore protected when DNSBL systems are employed.