What is a DNSBL or DNS Block List?
A DNSBL or DNS Block List is a list of IP addresses that have been identified as sources of unwanted or unsolicited email, also known as spam. These lists are used by email servers and other mail-related systems to filter and block incoming messages from known spam sources, in order to protect users from unwanted email. DNSBLs work by publishing a list of IP addresses that are known to be associated with spam, and then checking incoming messages against this list to determine whether they should be delivered or blocked. This can be used by email administrators to block spam from reaching their users, or by individual users to block spam in their personal email accounts.