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Re: "Header Reordering", yet again

2005-05-27 15:50:39

At 11:15 AM 5/27/2005 -0400, Bruce Lilly wrote:
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.

If we expect a guarantee, then no authentication method will work, not even signatures. There will always be systems that don't comply with any standard. The key question is can we expect enough compliance that authentication will be useful? We don't expect every sender to be compliant, just the ones that want to be trusted as Public Mail Servers. This may be a small number at first. Then others will discover the benefits of becoming compliant - bypass the spam filtering.

> Furthermore:
>     """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)).

If the non-SMTP hops are in private networks, we don't need to look inside their mail structure. They will present an ID at their gateway to the Public Internet, and it is that ID that gets rated.

How much of the Public Internet mail transfer (not including private networks) is non-SMTP? Where would these "bubbles" fit in Dave Crocker's mail architecture Protocols and Services diagram?

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.

Again, this sounds like "internal stuff" that we don't need to look at. Any server that wants to be a trusted Public Mail Server must follow the rules, whether they are an SMTP MTA, an X.400 MSA, or a Gameboy. The final receiver will step back through the authentication headers, skipping maybe one or two trusted forwarders, then to the Identity which will be rated.

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.

Do these strange systems occur as forwarders on the Public Internet? A receiver can do whatever it wants with the headers on its own incoming mail. It can even pay its own forwarder to re-arrange headers on incoming mail. If that forwarder re-arranges headers going to other customers, however, it will lose its status as a Trusted Forwarder.

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