[ietf-dkim] Discussion of Consensus check: Domain Existence Check

[Charles Lindsey]

On Tue, 10 Jun 2008 18:34:57 +0100, Douglas Otis <dotis at mail-abuse.org>  
wrote:

> On Jun 9, 2008, at 9:21 PM, Jim Fenton wrote:

>> Since it apparently isn't clear:  I am proposing retaining the
>> NXDOMAIN domain validity check as a MUST.  It is only the MX and A/
>> AAAA check that I'm proposing be changed from a SHOULD to a MAY.
>
> The situation created by MS Exchange creates a problem where just an
> NXDOMAIN check is still problematic.  While NXDOMAIN might occur for
> any leaked X.400 address or typical "somebody at something.invalid",
> NXDOMAIN results might also occur with any proxy SMTP addresses
> assigned by MS Exchange.  This occurs since MS Exchange assignments
> and routing do not depending upon DNS records.  Such an NXDOMAIN test
> would disrupt messages created by the company where I work, for
> example.  In addition, unless the test goes one step further to
> determine whether a domain appears to support SMTP, this would offer
> far less utility in preventing address spoofing.  Nor could just an
> NXDOMAIN test offer protection for non-SMTP domains.

But you have repeatedly failed to explain how a verifier could recognise  
and handle this case in a manner that did not leave a loophole for all the  
scammers and spoofers to walk through. If some message arrives with a From  
that includes a proxy SMTP address assigned by MS Exchange (which will  
surely result in NXDOMAIN), what do you want the Verifier to do? Is there  
some way that is can recognise this as a proxy address and let it through  
whilst still rejecting things apparently from the domain funny.ebay.com?

If some companies using MS Exchange allow such messages to escape, then I  
am afraid that is just Tough! It is a stupid behaviour. I might accept  
that domains whose TLD clearly did not exist could be exempted from the  
NXDOMAIN check in ADSP.

And what do you mean by a "non-SMTP domain. AKAIK the phrase is  
meaningless.

-- 
Charles H. Lindsey ---------At Home, doing my own thing------------------------
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