Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!att!linac!midway!gargoyle!chinet!les
From: les@chinet.chi.il.us (Leslie Mikesell)
Newsgroups: comp.mail.misc
Subject: Re: Which headers may Sendmail re-write?
Message-ID: <1990Dec26.170227.20484@chinet.chi.il.us>
Date: 26 Dec 90 17:02:27 GMT
References: <27710AE7.1356@tct.uucp> <1990Dec21.193938.29940@chinet.chi.il.us> <27763742.4907@tct.uucp>
Organization: Chinet - Public Access UNIX
Lines: 55

In article <27763742.4907@tct.uucp> chip@tct.uucp (Chip Salzenberg) writes:

>For all these reasons, I will always use Reply-To: and From: addresses
>-- or if they've been munged, signature addresses -- rather than the
>From_ line.  The From_ line is unsuitable anyway, because it is a path
>to the *sender*, who is not necessarily the user to whom replies
>should be sent.

From the recipient's point of view it is impossible to tell if a header
line has been munged or not.  Thus your basis for choosing how to
reply has a fatal flaw.

>Thus, to get back to our original subject, it is Evil and Rude to mung
>an RFC822 address from user@valid.domain into valid.domain!user,
>because such munging renders impossible the *correct* handling of
>replies for RFC822-aware but UUCP-only sites.

I disagree here, although prepending a hostname makes any futher
intelligent handling impossible.

>But, as you note in an unquoted portion of your
>article, bang notation is relative, whereas RFC822 notation is
>absolute.  Thus @-to-! translation is a semantic change, not just a
>syntactic one.  Therefore, gratuitous conversion of addresses from
>absolute to relative is (all together, now): Evil and Rude.

That's not quite what I said.  I said uucp addresses are relative.  The
distinction between @ and ! notation is purely syntactic and a sensible
MTA will be able to convert user@domain/domain!user (or a!b!c!d to
@a,@b:d@c) transparently.  The significant difference between relative
and absolute addressing is whether the machine where the address was
originally written and the machine interpreting it currently share a
common naming service.  On a uucp machine, that is only known to be
true if both happen to be the same machine.  As a matter of practicality
you may want to interpret the existence of a dot in the machine name
to mean that you can pretend that there can only be one such machine
that you or some forwarding machine can identify specifically. (And of
course internet forwarders that drop .uucp from headers blow away
this choice...)  Otherwise the only way to get it right is to send it
back to the originating machine for interpretation (though it should
be safe to chop out any a!b!a hops).

This is strictly a UA issue though, since we are talking about taking the
header addresses and doing something useful with them.  As long as the
From_ line contains a path to the sending machine and the other header
lines contain more or less what the sender put there, the UA can construct
working addresses of any form (!-path relative to sender, domain!user,
path!to!smarthost!domain!user, etc.) based on it's best interpretation
of what the original address meant at the sending machine.  Note that
if you deal with attmail you will get header lines with uucp paths
that must be interpreted relative to the sending machine so pretending
that everyone is one big happy RFC822 family is not possible.

Les Mikesell
  les@chinet.chi.il.us