On May 26, 2010, at 12:59 PM, Steve Atkins wrote:

> On May 26, 2010, at 7:45 AM, Brett McDowell wrote:
> 
>> On May 25, 2010, at 8:43 PM, Scott Kitterman wrote:
>> 
>>>> Like I said, "throw away anything that doesn't have our signature" has 
>>>> some chance of broad adoption.  Every extra word you add to the message 
>>>> makes it less likely that people will do it.
>>>> 
>>> I agree with this. I have yet to see any proposals for additions that 
>>> didn't either add enough complexity to act as a barrier to deployment or 
>>> alternately make it trivially possible to allow third parties to create 
>>> messages that render discardable moot. 
>> 
>> I agree that adding anything to "throw away anything that doesn't have our 
>> signature" add complexity to implementation and therefore, by definition, is 
>> a barrier to adoption.  That's not what we are debating.  What we are 
>> debating is whether such complexity is a necessary evil that we should 
>> provide a specification to support -- as an optional mechanism for 
>> stakeholders who want to opt-in to the authenticated email ecosystem.  I 
>> *think* the answer is "yes".  But we haven't yet had the meaningful debate 
>> that will resolve that question.
>> 
>> Let's debate whether transient trust through a MLM is actionable.  Would a 
>> new header that enabled the MLM to report to the receiver that they indeed 
>> validated the original signature actually make any difference in the 
>> deliverability of that message to the receiver, and if yes, is that actually 
>> a good thing?  I say "yes" and "yes".  But I expect that if we debate this 
>> specific point one of you might highlight an unintended consequence that 
>> would tip the balance away from pursuing such a model.  
>> 
>> Thoughts?
> 
> Aesthetically I like the idea of some way for the MLM to tunnel 
> authentication information through to the recipient.

Perhaps that's common ground we just discovered.  Let's build on that.

> 
> But I don't think it's clear that doing so would change anything at the 
> recipients MX. As a concrete example, if two subscribers to a mailing list 
> send mail to the list, one DKIM signed and one not, and the list then signs 
> each message and sends it to the recipient, is there any reason that the 
> recipients MX would treat those two messages differently?
> 

Yes.  But we need more information about the scenario in order to describe how. 
 The following detail will illustrate how.

A = sender of message from an ADSP=discardable domain but the message was not 
DKIM signed
B = sender of message from an ADSP=discardable domain and the message was DKIM 
signed
C = the MLM who is a participating MLM in the authenticated email ecosystem
D = receiver of email from the MLM who is a participating receiver (DKIM/ADSP 
inbound)
Note: this scenario takes place in after this IETF DKIM WG standardizes the new 
header I mentioned above.

In this scenario C will report to D that the message from A was not signed on 
inbound and that the message from B was.  This would lead D to deliver the 
message from B but not deliver the message from A.  The MLM signed both 
messages before sending to D.

-- Brett


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