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Path: utzoo!watmath!clyde!bonnie!akgua!whuxlm!harpo!decvax!decwrl!sun!gnu
From: gnu@sun.uucp (John Gilmore)
Newsgroups: net.mail,net.mail.headers
Subject: Re: From lines in mail headers
Message-ID: <2263@sun.uucp>
Date: Sun, 2-Jun-85 21:36:08 EDT
Article-I.D.: sun.2263
Posted: Sun Jun  2 21:36:08 1985
Date-Received: Thu, 6-Jun-85 01:19:13 EDT
References: <487@bonnie.UUCP> <757@plus5.UUCP> <507@down.FUN> <155@jendeh.UUCP>
Organization: Sun Microsystems, Inc.
Lines: 23
Xref: watmath net.mail:886 net.mail.headers:466

> regarding hokey's assertion that "[t]here is no redundant cbosgd in
> [cbosgd!cbosgd.ATT.UUCP!db] line," this is transparent doublespeak.
> ...there is no logical reason to name cbosgd twice in the route...
> 	peter

Peter is correct; there is redundancy here.

The first cbosgd! is for dumb mailers.  If they need to send a reply
back, they will just pull off the first name and ! and route the message
there.

The cbosgd.att.uucp part is for smart mailers.  The convention is that
a string between ! chars which contains a period is a fully-qualified
domain based address.  Whenever a smart uucp mailer sees this address,
it can discard all the leading host!host!host! stuff and just use the
domain based address.

The reason both are there is that a smart mailer can't tell that
"cbosgd!db" is the same as "cbosgd.att.uucp!db", since there may be
many machines named "cbosgd" in different domains.  [If the smart
mailer is a neighbor of cbosgd's, it will know the full name of its
neighbor, but if the message has gone through some dumb intermediate
sites, it has no way to know.]