[ietf-dkim] Attempted text for x=

[Douglas Otis]

On Apr 20, 2006, at 11:34 AM, Jon Callas wrote:

> On 19 Apr 2006, at 10:14 AM, Paul Hoffman wrote:
>
>> What is the interoperability or harm-limiting purpose of verifiers  
>> checking x= values? If there is none, the sentence above needs to  
>> be a MAY.
>
> I don't want to torture people with my reasoning, but x= needs to  
> be a MAY, but for possibly different reasons.
>
> My reasons are that I don't think that an implementer needs to  
> "carefully weigh" whether to implement x=. I think that casually  
> weighing it is just fine. I've been thinking a lot about uses for  
> x=, and some of them might allow someone to game DKIM against other  
> parts of a mail filtering system. And yes, I know that this comes  
> close to conflating SHOULD-implement vs. SHOULD-deploy, but I would  
> not think ill of an implementor whose decision was "I don't  
> understand it well, so I'm not implementing it," which is the  
> antithesis of SHOULD.

The jabber chat concluded MAY...

There is also a downside ignoring x= when forwarding mail.  Safe  
solutions for this involve changing the way MTAs operate.  Gaming is  
also possible when not paying attention, especially when invalidated  
signatures offer a basis for rejection.  When this happens down- 
stream, MTAs not paying attention will be left dealing with DSNs.

-Doug