On Mon, Nov 3, 2025, at 10:28, Wei Chuang wrote:
> While I understand the desire to keep DKIM2 simpler, pp= permits delegation 
> to an email hosting provider as already pointed out above.  One consideration 
> I didn't think of till now is this pp= delegation can help with the DKIM2 
> adoption especially when we consider the algorithmic agility requirement.  
> DKIM2 at some near point wants to mandate publishing and signing both with 
> RSA and ED25519.  My guess is that many senders and forwarders will have 
> trouble deploying ED25519, and one avenue to smooth adoption is allowing them 
> to delegate publishing and signing to their platform.  That said, I noticed 
> that pp= has been removed in draft-clayton-dkim2-spec-03, so perhaps this 
> discussion is perhaps moot.

We need to discuss this point, it will be a major discussion point for the 
headers/

> Regarding the mv= tag, can more clarity be provided how that is different 
> from the i= instance number?  Is the idea that a more recent (higher i= 
> number) DKIM2 signature can reference an older (low mv=) MailVersion header?  

Sure, in my example, I have a message in which the same mv= is signed twice, 
then multiple new versions are created before signing again:

brong@elg:~/src/interop/brong$ perl validate.pl brong-final.eml
OK DKIM2-Signature: i=4; mv=5; s=sel3; d=test1.dkim2.com
OK Mail-Version: mv=5
OK Mail-Version: mv=4
OK Mail-Version: mv=3
OK DKIM2-Signature: i=3; mv=2; s=sel2; d=test1.dkim2.com
OK DKIM2-Signature: i=2; mv=2; s=sel2; d=test1.dkim2.com
OK Mail-Version: mv=2
OK DKIM2-Signature: i=1; mv=1; s=sel1; d=test1.dkim2.com
OK Mail-Version: mv=1

So there are two separate things here.  Versions of the email, and signatures 
on those versions.  Right now I'm not checking that the signatures chain with 
d/mf/rt alignment, which is why they need their own monotonically increasing 
series.

Bron.

--
  Bron Gondwana, CEO, Fastmail Pty Ltd / Fastmail US LLC
  [email protected]

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