Cypherpunk anonymous remailer

A Cypherpunk anonymous remailer, also known as a Type I remailer, is a type of anonymous remailer that receives messages encrypted with PGP or GPG, follows predetermined instructions to strip any identifying information, and forwards the messages to the desired recipient. Cypherpunk anonymous remailers are vulnerable to traffic analysis attacks, which take advantage of the predictable order in which messages are sent to recipients.

Source: Wikipedia — Cypherpunk anonymous remailer (CC BY-SA 4.0)