Glossary · Detection & reputation
IP blacklist
A published list of IP addresses flagged for abuse, which sites and mail servers consult to refuse traffic outright.
An IP blacklist is a shared record of addresses judged to have misbehaved, spam sources, fraud origins, known proxies, that services check to decide whom to refuse. Land on a widely used one and doors close before you knock, because the block is applied on the strength of the listing alone.
Listings are often collective and sticky. Frequently it is a whole subnet that gets listed rather than a lone address, so a clean IP can be refused for its neighbours' conduct, and getting removed is a process rather than an instant, which is why a fresh listing outlasts the behaviour that caused it.
For proxy work this makes provenance matter. An address from a network with a history of abuse is a liability regardless of your own use, and the practical defence is starting from clean, well-kept addresses rather than trying to rehabilitate tainted ones.
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