Re: [dmarc-ietf] WGLC ARC-16 concern on Section 5.1.2 - cv=fail should sign greedily

"John Levine" <johnl@taugh.com> Wed, 15 August 2018 18:30 UTC

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From: John Levine <johnl@taugh.com>
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Subject: Re: [dmarc-ietf] WGLC ARC-16 concern on Section 5.1.2 - cv=fail should sign greedily
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In article <799c2b18-97fe-6e22-f2cf-49245ae9c65e@gmail.com> you write:
>So the extra mechanism is intended an efficiency hack.

No, it also documents the fact that the chain was broken when it
arrived at the cv=fail signer.  Without it, a subsequent hop can't
tell.  It probably won't make much difference to spam filters, but
it could be useful if you're trying to find and fix forwarders
that make gratuitous changes.

I think there's a modest benefit to signing with cv=fail, and since
you can't count on having a chain (even an invalid one) signing as
if it were cv=none seems reasonable.

R's,
John

PS: Once there is a cv=fail seal, there doesn't seem to be any point
to adding any more seals in later hops.  It's dead, Jim.