[ietf-dkim] Signalling DKIM support before DATA
dotis at mail-abuse.org
Tue Aug 8 12:55:32 PDT 2006
On Aug 8, 2006, at 12:25 PM, J.D. Falk wrote:
> On 2006-08-08 11:43, Scott Kitterman wrote:
>>> Sounds like false hope to me; as a big receiver, I can't imagine
>>> I'd ever want to blindly trust assertions made by an unknown sender.
>> As both you and John L point out, this is a big issue. That's why
>> I was thinking about it being something in DNS related to the
>> policy record so that it would be at least slightly harder to lie
>> about it. It's also why I started with IF... I recognized that
>> if it can be trivially spoofed, then there's no reason to do it.
> We can accomplish that much without any changes to SMTP:
> - SMTP conversation happens as per usual
> - receiver looks up MAIL FROM domain, checks SSP
> - receiver decides whether to accept the message and check the
> signature, or reject based on non-DKIM-related criteria
> Or am I missing something?
By SSP you mean the First-Party-Policy. A check subsequent to
receiving the entire message could verify there is an association
between the First-Party-Address and the Signing-Domain, but this is
not assured to match the MAIL_FROM. This implies that MAIL_FROM will
always have the same domain as that of the Signing-domain. A
separate MAIL_FROM policy could avoid this constraint. A MAIL_FROM
policy would offer greater value when it corresponds to the SMTP
client issuing the message rather than the signing domain.
Imagine a message signed by your domain is replayed from a system
controlled by a bad actor. How is this detected? A MAIL_FROM policy
could confirm there is a relationship with that of the client before
the message is accepted. Authenticating the client allows policy
(relationships) to be established between both the MAIL_FROM and the
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