> -----Original Message-----
> From: Michael Thomas [mailto:[EMAIL PROTECTED]
>
> Indeed, DKIM has the same constraint as well.  What I'm not entirely
> getting is why 4474 isn't sufficient for the overall goal.

That has been a source of debate for a couple years of mailing list traffic. :)
The problems identified so far, I think:
1) Most URI's are actually E.164's, either as Tel's in Sip disguise, or as real 
Tel's - and 4474 either can't apply to it, or shouldn't, or should - depending 
on who you ask and in what context.  But E.164 is the elephant in the room.
2) 4474 signs things which many real-world cases will break the signature of, 
and thus has a deployment problem (whether that's fixable, or by design, is 
another topic of debate).  But that's another elephant in the room, or maybe a 
lion, smaller but hairy.
3) 4474 is susceptible to cut/paste attacks - for example the baiting attack.  
That one's more like a clown, annoying but probably not deadly.
4) 4474 requires 4916 for called-identity, which some people aren't happy with 
I think.  That one's more like a camel, a hump some people don't like the smell 
of.

At least I think that's the main tent.  So basically what we got here is a 
circus, with some of us trying to tame the animals, while others prefer to sit 
and enjoy the show. :)

-hadriel
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