[Mimedefang] X-Auto-Response-Suppress header

kd6lvw at yahoo.com kd6lvw at yahoo.com
Mon May 21 21:28:38 EDT 2012

--- On Mon, 5/21/12, George Roberts <groberts at purity.net> wrote:
> I'm sort of sorry I started this
> whole thing, LOL. Just so I have some clarity on the issue,
> could someone please explain to me what exactly it is that
> Exchange does with Received: headers that is so bad?  I
> see Received: lines from various mail systems and they all
> seem to me to be a little bit different. Also, if possible,
> please state which RFC dictates the format Exchange is
> accused of breaking.
> Just trying to understand what the issue is.

RFC 821 and its successors and add-ons through to 5321.

It places a multi-word phrase after "with", while "with" takes a single word called an "atom" in the syntax.  Sometimes, it also generates "id" field parameters which contain periods when they are not bracketed with greater-than/less-than and contain an "@" (i.e. an "addr-spec").  Basically, they don't follow the required syntax and are therefore in error.

If exchange didn't use SMTP, there would be no problem with its "Received:" headers since the stricter syntax of RFC 5321 wouldn't apply, and these do meet the weak syntax of RFC 5322 (which applies to NON-SMTP messages).

When "with" is present, its parameter must be on the list of IANA registered values.  When "with SMTP" (or a variant) is present, RFC 5321 governs the REQUIRED syntax of the "Received:" header (which includes mandatory "from" and "by" clauses, etc., ...).  "with Microsoft SMTPSVC" simply isn't valid.

Exchange uses SMTP but generates a syntactically incorrect header.  Similarly with Google's gmail (it often omits the "from" clause when required), Yahoo's use of an unregistered protocol ("with NNFMP"*), qmail, and of late, exim.

* - When Yahoo was asked about NNFMP, its help-desk staff indicated in 2009 that any message which contains it is not real but a forgery.

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