Pseudonymous remailer

Definition
A pseudonymous remailer is

"[a]n Internet computer service that launders the true identity of an e-mail sender by replacing the sender's e-mail address with a false one (i.e., pseudonymous address) and forwarding the message to the intended recipient. A recepient's reply is sent to the sender's pseudonymous address, which, in turn, forwards the response to the sender's true address."