An anonymous remailer is a computer which has been configured to run
remailer software. This software is a specialized kind of email server
software. Unlike the average email server which goes to great lengths
to log all incoming/outgoing traffic and add identifying and traceable
info to its outgoing mail (in the form of headers) remailer software
ensures that outgoing mail has been STRIPPED CLEAN of any identifying
information! Thus the name 'anonymous' remailer.

The remailer performs certain automated tasks which include retrieving
mail, decrypting/processing that mail (only mail that is properly
encrypted and formatted), obeying the directives within the message
and, finally, delivering - remailing - the finished product to a
second party in anonymized form. When received by that second party it
will reveal only that it was sent from an anonymous source (usually
the remailer's name and email address). The IP address shown will be
the IP address of the remailer machine.

Ideally, no logs are kept by the remailer software. This ensures both
the anonymity of the user and protects the operator from liability.
(See Mike Shinn's work in progress FAQ For Remailer Operators
<http://mixmaster.shinn.net/faq/index.html>.)

The process is not completely automated since a human operator is
required - called a remailer operator, or RemOp - to ensure that
traffic is running smoothly, that PGP and Mixmaster encryption keys
are kept updated, that complaints of abuse are dealt with, and also
that users and fellow operators are kept up to speed on any changes to
the remailer's configuration. APAS is the place where such updates are
posted. They are also posted to the Remailer Operator's Mailing List
(Blank email to remailer-operators-request@anon.lcs.mit.edu for
details on how to subscribe.) There is also an archive of the Remop's
List <http://lexx.shinn.net/mailman/listinfo/remops>. You can even
post to the list from this Web page! (Thanks Mike Shinn.)

That's basically how a remailer works. Some anonymous remailers can
send both email and newsgroups posts. And most will require newly
arrived messages to be encrypted. More about that later.  See also:
Andre Bacard's Remailer FAQ <http://www.andrebacard.com/remail.html>
and William Knowles' overview of anonymity on the 'Net
<http://www.c4i.org/erehwon/anonymity.html>.