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From: huitema@jerry.inria.fr (Christian Huitema)
Newsgroups: comp.mail.misc
Subject: Re: Which headers may Sendmail re-write?
Message-ID: <9389@mirsa.inria.fr>
Date: 7 Dec 90 13:01:01 GMT
References: <208@frcs.UUCP> <1990Dec6.042257.9620@blilly.UUCP> <KARL.90Dec6171155@giza.cis.ohio-state.edu> <1990Dec7.003726.28242@mp.cs.niu.edu>
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Reply-To: huitema@jerry.inria.fr (Christian Huitema)
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In article <1990Dec7.003726.28242@mp.cs.niu.edu>, rickert@mp.cs.niu.edu (Neil
Rickert) writes:
> In article <KARL.90Dec6171155@giza.cis.ohio-state.edu>
> karl_kleinpaste@cis.ohio-state.edu writes:
> >If your site inflicts "user@tinytoy" on my sendmail, I'm going to
> >finish the job of address-breaking that your site started: It's going
> >to be rewritten as user@cis.ohio-state.edu.  This rewrite does the
> 
>  But if your site inflicts 'user@tinytoy' on my sendmail, its gonna
> be changed to 'user%tinytoy@your.relay.host', where 'your.relay.host'
> means the host which actually connected to me - if not known to DNS
> this might become 'user%tinytoy@[1.2.3.4]' (with the appropriate actual
> internet address.
> 

There are two cases to consider: submission and relay. Submission is performed
when a local user edit a piece of text, using some more or less adequate tools
ranging from "ed" to "xmh", and "pipe" it into the "mailer". Relay is performed
when a host on the network receive a piece of mail from another host, and ask
the local host to relay or deliver it.

In the case of relay within a single network, or more precisely within a single
naming system, there is no reason to muck with anything but the envelope. In
fact, any attempt to "correct" or "rewrite" the addresses in lines like "from"
or "to" or "reply-to" is just bound to add noise and augment the occurence rate
of irrepliable address: if the information was not correct from the beginning,
it will probably stay incorrect after a rewrite. And if it was correct, it may
well become incorrect. In short, the philosophy relies on the difference
between names and addresses: names should be absolute, and should be the only
thing present in headers, whilst using overwriting the names with addressing
information using either the "!" or the "%" or the <@,@,@:> convention might be
a fair game in the envelopes.

On the other hand, a local mailer should make sure that the pieces of texts
submitted by the suers are actually valid pieces of mail. This may involve
checking the names in some headers to ensure that they are valid FQDN, and
checking that the mandatory or semi mandatory fields "Date", "From" and
"message-id" are present.

One of the problems with sendmail is that one cannot specify in the ".cf" file
which actions are to be performed on a "real" and which on a "submission".

Christian Huitema