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Re: (lack of) message header field ordering

2005-03-13 14:42:43

On Sun March 13 2005 15:09, Tony Finch wrote:

   OTOH, there _might_ be some existing MTA this would break, though I
can't think why...

It might confuse software that analyses Received: fields, causing it to
fail to find all of them. However there is plenty of software out there
which already interleaves other fields amongst Received: fields, so robust
code already has to cope with it.

Any software that attempts to analyze Received fields is the work
of a misguided author and is unlikely to be useful.  RFC 1123 notes
that:
              Received: lines are primarily intended for humans tracing
              mail routes, primarily of diagnosis of faults.  See also
              the discussion under 5.3.7.
and
                   Received: fields of messages originating from other
                   environments may not conform exactly to RFC822.
                   However, the most important use of Received: lines is
                   for debugging mail faults, and this debugging can be
                   severely hampered by well-meaning gateways that try
                   to "fix" a Received: line.

Aside from the "other environments", there exist widely-deployed
agents that generate Received fields which do not conform to even
the very liberal syntax of RFC 2822.  E.g:
   Received: from mail pickup service by crm with Microsoft SMTPSVC;
         Fri, 4 Mar 2005 16:55:49 -0800