Re: [dmarc-ietf] ARC questions

["Kurt Andersen (b)" <[e-mail]>]

As usual, John has pretty well nailed the response, but there was one other
part of your question (Mike) that I thought deserved explanation:

On Sat, Nov 21, 2020 at 7:14 PM John Levine <[e-mail]> wrote:

> In article <[e-mail]> you write:
> >If I'm a receiver who is going to be making some filtering decisions
> >based on ARC, I see that it passed by some authenticator along the way
> >which is fine, but my question is why I should trust that intermediary
> >in general?
>
> The short answer is that you shouldn't, any more than you should trust
> random DKIM signatures.
>
> This also means that ARC isn't useful if you don't have a reputation
> system to tell you where the lists and other forwarders that might add
> legit ARC signatures are.
>

On Sat, Nov 21, 2020 at 2:33 PM Michael Thomas <[e-mail]> wrote:

>
> Or did I miss where ARC resigns the body? Or is there a tie in for ARC
> with the mailing list's resigned DKIM signature for the new message?
>

The ARC-Message-Signature (referred to as the AMS) includes a signature
over the newly modified message (headers & body) in a way very similar to a
DKIM-Signature. But this does not solve the problem of a malicious
forwarder that does a wholesale replacement of the (presumably) good
content with spam. That's were your own reputation and content analysis has
to come in.

--Kurt