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From: jik@athena.mit.edu (Jonathan I. Kamens)
Newsgroups: comp.mail.sendmail
Subject: Re: Need to fake return machine address
Message-ID: <1990May25.192431.6904@athena.mit.edu>
Date: 25 May 90 19:24:31 GMT
References: <1990May21.181455.22689@mozart.amd.com>
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Reply-To: jik@athena.mit.edu (Jonathan I. Kamens)
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  Project Athena has a similar problem.  We have almost 1000 public
workstations, none of which receive mail locally; however, mail sent
from them goes through sendmail, and the addresses of local users have
to have "@ATHENA.MIT.EDU" tacked onto the end of them.  We accomplish
this by doing the following:

1. Outgoing mail from a workstation is run through a *very* bare-bones
cf file which is capable of delivering only mail that is explicitly
marked LOCAL or POP (e.g. user@host.LOCAL).  Since most workstations
aren't configured for local accounts or for pop, the LOCAL and POP
delivery lines in the cf file are very rarely used.

2. Any mail that is not LOCAL or POP is forwarded to the mailhub for delivery.

3. The mailhub takes "@ATHENA.MIT.EDU" onto any address that has only a
username on it, then continues with mail delivery.

4. There is a huge automatically generated aliases file on the mailhub
which says where incoming mail is supposed to go.  This includes all the
mailing lists, and all the post-office addresses for users (mail isn't
stored for everybody on the mailhub; it's stored on several post offices
from which users pick up their mail using Kerberized POP protocol).

  Now, an example.  Let's say I'm on workstation w1, and I send mail
with a To: address of "joeruser".  Here's what happens:

1. The local cf sees that the message isn't LOCAL or POP, so it forwards
it to ATHENA.MIT.EDU, the mailhub.

2. The mailhub sees the "joeruser" and changes it to
"joeruser@ATHENA.MIT.EDU".  It also changes the from address from "jik"
to "jik@ATHENA.MIT.EDU", since the local cf doesn't add the workstation
address to my address.  The "@ATHENA.MIT.EDU" stuff is added both in the
message text and internally.

3. The mailhub then realizes that the joeruser address is local after it
strips off the @ATHENA.MIT.EDU internally (but not in the message text),
and finds the post office address for joeruser in the aliases file, and
delivers it.

  You can use a similar mechanism, on a smaller scale, to channel all of
your mail through one machine with a big aliases file.  Note, however,
that this scheme makes it difficult to send mail directly to a machine
participating in this scheme, because the machine is going to want to
forward the message to the mailhub unless you end the message in LOCAL.

  If there is some interest, I can post our workstation and mailhub cf
files (or, at least, all of the relevant parts -- I don't think I need
to post the standard canonicalization stuff).

Jonathan Kamens			              USnail:
MIT Project Athena				11 Ashford Terrace
jik@Athena.MIT.EDU				Allston, MA  02134
Office: 617-253-8495			      Home: 617-782-0710