Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!cis.ohio-state.edu!karl_kleinpaste
From: karl_kleinpaste@cis.ohio-state.edu
Newsgroups: comp.mail.misc
Subject: Re: Which headers may Sendmail re-write?
Message-ID: <KARL.90Dec13123956@giza.cis.ohio-state.edu>
Date: 13 Dec 90 17:39:56 GMT
References: <2766B2E7.276@tct.uucp>
Sender: news@tut.cis.ohio-state.edu
Organization: Ohio State Computer Science
Lines: 71

chip@tct.uucp writes:
   2.  A message passing through your domain on its way to my domain
       should be left alone, without ANY modifications to the message
       AT ALL except for the envelope.

   No site causes problems for other sites by following these rules.
   So why shouldn't we all adopt these rules right now?  I'm listening...

I doubt it.  Pardon me for being rude, but I really doubt it.

A hypothetical example.

Let's assume that "tct" is a UUCP neighbor of "osu-cis."  Let's assume
that chip@tct.uucp sends mail aimed at, say, osu-cis!ucbvax!somebody.
Headers read:
	From: chip@tct.uucp
	To: osu-cis!ucbvax!somebody
Envelope looks like "From tct!chip" and "rmail ucbvax!somebody" by the
time it reaches my system.  So far, so good, I hope.

My mail installation wants to do things to reach ucbvax via the
Internet rather than UUCP.  That is, seeing "ucbvax!somebody" as an
intended destination, I nonetheless want to speak SMTP to
ucbvax.berkeley.edu.  This is perfectly legit, as the choice of
outbound transport is mine to make.

I _can't_ send
	MAIL FROM:<tct!chip>
in SMTP because it lacks "@right.hand.side" as required by the RFCs.
MAISER on a DEC-20 will choke (has choked) on it.  Nor can I send
	MAIL FROM:<chip@tct.uucp>
as the envelope origin.  "uucp" is not a valid top-level domain.  See
RFC 1123 section 5.2.2 page 49.

I _can't_ send
	From: chip@tct.uucp
in the headers.  "uucp" is not a valid top-level domain.  Similarly,
	From: tct!chip
is insufficient due to no "@right.hand.side."  See RFC 822 in several
places, such as the syntax grammar beginning section 4.1 page 17: the
"mailbox" spec must be properly dealt with.

Do you see a pattern developing here?

I hack headers as well as envelope because headers containing bogon,
unreal, and unregistered domains are invalid on the Internet.  Your
headers, as supplied to my mailer, are WRONG.  You CANNOT count on any
random site anywhere on the Internet being able to reply to such an
address.  Keep in mind that, regardless of what envelope hacking gets
done, legitimate replies end up going to the From: address.  And there
are rather more sites out there incapable of addressing "host!user"
than you might think.

I generate RFC-compliant headers when speaking to Internet sites.  So
I will generate the following SMTP conversation to ucbvax.berkeley.edu
for this mail:
	HELO something.cis.ohio-state.edu
	MAIL FROM:<tct!chip@cis.ohio-state.edu>
	RCPT TO:<somebody@ucbvax.berkeley.edu>
	DATA
	From: tct!chip@cis.ohio-state.edu
	To: ucbvax!somebody@cis.ohio-state.edu

	your text
	.
	QUIT
That works.  Nothing else does.  (Well, I could have rewritten the To:
as somebody@ucbvax.berkeley.edu, but my .cf isn't quite smart enough
to do that at that level.)  And it was *necessary*.

--karl