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Re: "Header Reordering", yet again

2005-05-27 08:15:20

On Fri May 27 2005 10:09, David MacQuigg wrote:

At 01:05 PM 5/23/2005 -0400, Bruce Lilly wrote:

Except for a few inconvenient facts:
a) "It is important to note that the header fields are not guaranteed to
   be in a particular order.  They may appear in any order, and they
   have been known to be reordered occasionally when transported over
   the Internet." RFC 2822, section 3.6

Here is the complete quote:

That doesn't change the fact that there is no guarantee, and that any
assumption of a particular order is flawed.

    """When an SMTP server

Not all transport is via SMTP (while a given entity may use SMTP, there
is no guarantee that *ALL* preceding "hops" in the store-and-forward
transport chain used SMTP (nor, that *ALL* SMTP hops were conformant to
RFC 2821, a Proposed Standard)).  Moreover, specific exceptions are granted
to gateways and MSAs, and there is no reliable way to determine if an SMTP
receiver operating on port 25 is a gateway or MSA; there are no gateway- or
MSA-sepcific response codes nor are there any ESMTP keywords that indicate
to a client "this is a gateway" or "this is an MSA".  There is certainly
no way that a subsequent analysis of the message can make any kind of
reliable assessment of whether or not any receiver that putatively handled
the message in transit was a gateway or MSA.

And by the time one has a message in a place where it can be examined, it
might not even be in the Internet Message Format per se.  I am told (but
have no independent confirmation) that systems such as Lotus Notes and
Microsoft Exchange do not indicate (to applications accessing content
for filtering) field order.