IP blacklist

An IP blacklist is a database or list of IP addresses that should be blocked from connecting to a protected system. These blacklists (aka blocklists, blackhole lists, or DNSBL's) are most commonly used by email receivers to screen out spam and other abusive emails flooding the Internet.

The best IP blacklists use "honeypots" to detect new sources of abuse, and publish the source address within hours. Honeypots have addresses that are never used in a legitimate email, but are posted on various websites and other locations where criminals typically "harvest" addresses. IP blacklists are most useful in efficiently blocking high-volume and persistent sources.