Trusted by data scientists, security experts, and anti-spam professionals, Enemieslist (EL) protects over 3.6 billion users from online abuse. EL works by classifying hostnames (PTR records) in order to allow policy to be applied in various contexts. Originally intended to aid in the risk evaluation of accepting mail from a given host, Enemieslist's unique approach and comprehensive coverage now finds applications beyond anti-spam. Our classifications find use in reputation services, anti-fraud, anti-abuse, anti-spam, threat detection, information security, network security, calibration of data sets, and priming machine learning systems.