[Mimedefang] Received headers in general

[Les Mikesell]

On Wed, May 23, 2012 at 1:49 PM,  <kd6lvw at yahoo.com> wrote:
>
>> I disagree.  You are projecting your interpretation on the RFC authors.
>> They say you MUST NOT reject a message for a bad trace header.  It further
>> says that one reason for bad trace headers is non-SMTP systems.  It does
>> not say it's OK to reject because of a bad trace header from an SMTP system.
>> You're reading text that isn't there.
>
> Wrong.  It directly states that we can't reject on the basis of trying to enforce SMTP trace header syntax upon non-SMTP trace headers.  That is all.

No.  The exact quote:
  "As another consequence
   of trace header fields arising in non-SMTP environments, receiving
   systems MUST NOT reject mail based on the format of a trace header
   field and SHOULD be extremely robust in the light of unexpected
   information or formats in those header fields."

There is a justification, but no qualification at all on the MUST NOT reject.

> As noted, I don't apply the stricter checks to non-SMTP-claimed messages, so I am in fact following this section of RFC 5321.

But you said you applied them to Exchange-originating messages, which
is a non-SMTP environment.

>
> Precisely, and as spammers often generate non-compliant messages, a RFC 5321 compliance filter installed into an MTA is a valid anti-spam measure.

That doesn't match my experience.  Spam senders are extremely
sophisticated and much more likely to pay attention to the exact
syntactic details than the big companies with the 'we don't follow
standards, we make them'  attitude.

-- 
   Les Mikesell
     lesmikesell at gmail.com