This file started life (but modified since) as my post:

>Date: Sat, 21 May 1994 20:53-EDT
>From: Vincent.Cate@FURMINT.NECTAR.CS.CMU.EDU
>To: cypherpunks@toad.com, outnews+netnews.alt.security.pgp@andrew.cmu.edu
>Subject: "Email-Firewalls" / Instant Corporate PGP


Companies like the idea of firewall machines to protect the security of
their internal nets.  I bet they would also like something called an
"email-firewall".  Names are important. :-)  I think of the
email-firewall as a slightly modified anonymous-remailer.

Outsiders could send encrypted mail to the remailer and it would
decrypt it and send it on to the right person inside the company over
internal (more secure) nets.

The email-firewall could also encrypt outgoing mail when it was going
to a person who either had a listed PGP key or who was working at
another company with an email-firewall.

With this the average user inside the company would not need to deal 
with the encryption directly.  A system administrator would set things
up without users needing to learn anything.  Getting encrypted mail would 
not take anything new, and sending might take a slight change.

This remailer would make email somewhat anonymous as far an outsider
looking at mail, since it would all be going to or coming from one
account name.  However, this remailer would not hide the identity of
the sender from the person receiving the mail (so it is not a typical
anonymous remailer).  Corporations need security, but probably not 
anonimity.  

Each company would only need to buy one copy of ViaCrypt PGP.  For a
company this cost is, of course, negligible.

Of course this is only a step towards true end-to-end encryption, but
it is easy and far better than what they have now.  Also, it fits with
the way companies work.  There is a security guard at the entrance to
the plant, but once inside people generally trust each other and don't
worry about security.  With this, internal mail is still like
postcards, but external would have an envelope.  

I thought about this when making two short scripts (below) that let
me send and receive mail without any extra work.   Mail to 
vac+pgp@cs.cmu.edu (my low security envelope) is decrypted 
automatically.  To send mail I make aliases like "vac+eric" in 
my .maildelivery and when I send to them they are encrypted and then 
resent to the right place.

These 2 scripts are not the full "email-firewall" - but a step in
that direction.  Thought I would throw the idea out.  Has anyone done 
this?   Let me know if you do.  Future info I get on email-firewalls 
will go into this file:

    http://www.offshore.com.ai/security/email-firewalls

My send and receive scripts are:

    http://www.offshore.com.ai/security/pgp-send
    http://www.offshore.com.ai/security/pgp-receive

  -- Vince