Re: [dmarc-ietf] Reports helping spammers? (#81)

Not sure what is unclear about my concern.

The spec provides for reporting whether the actual disposition was
different from the sender policy request, and the reason that this was done.

Ale suggests that "disposition" must be narrowly defined to mean only the
disposition based on DMARC staus.  This still means that local policy is
revealed under some circumstances.

I do not see why local policy should be revealed at all.

On Fri, Jan 22, 2021, 8:41 AM Todd Herr <todd.herr=
40valimail.com@dmarc.ietf.org> wrote:

> On Fri, Jan 22, 2021 at 7:00 AM Douglas Foster <
> dougfoster.emailstandards@gmail.com> wrote:
>
>> My specific concern is with disposition information.    Whether the
>> message presents with acceptable credentials is the sender's
>> responsibility, and I have no problem with documenting whether it passed
>> SPF or DKIM or both, including which DKIM scope was used for the
>> evaluation.     I have no problem with reporting the sender policy that I
>> retrieved from DNS.
>>
>> But should I report the disposition applied, and the reason that my
>> disposition was different from the sender policy?    That seems like
>> information leakage about my defenses which should only be revealed to
>> highly trusted correspondent domains.
>>
>> Consider what is likely to happen If I call an organization's help desk
>> and say,
>>      "My emails to Sally are not getting delivered, and I want to know
>> why?"
>> The answer should be, and usually is,
>>      "Have Sally open a ticket and we will discuss the problem with her!"
>> Should not the same policy apply here?
>>
>
>
>
>>
>> Possible misuse of disposition information:
>> - DMARC=(Fail), Disposition = (120 delivered) -- probably means that my
>> system does not enforce DMARC at all
>> - DMARC=(Pass), Disposition = (20 delivered, 100 rejected)  -- possibly
>> means that my system needs 20 messages to learn how to identify bad content
>>
>> I suggest that disposition information should be redacted by default, and
>> only included on an exception basis for highly trusted source domains.
>>
>>
> You're using the phrase "disposition was different from the sender policy"
> in a way that I don't understand.
>
> Sender policy is a request for handling when a message fails DMARC
> validation checks. In your examples of possible misuse of disposition
> information, one you're citing is 100 rejected messages when DMARC passes;
> that's not a disposition that's different from sender policy, because DMARC
> pass is no guarantee of a message being accepted, and again, sender policy
> only concerns the state of DMARC failing validation checks. The DMARC
> policy statement isn't a vehicle for requesting handling when the message
> passes DMARC checks. Beyond that, I'm not even sure that a condition exists
> where a message would have a disposition of "rejected due to DMARC" when
> the DMARC validation result is pass, but I've been accused in the past of
> lacking imagination, so perhaps it could happen.
>
> For your example of DMARC failing and all 120 messages being delivered,
> I've never personally met a spammer (every conversation I ever had started
> with "I'm not a spammer")  but I can't conceive of a spammer configuring
> his domain with a DMARC policy of p=reject and sending mail that doesn't
> authenticate as a way of probing things, but I suppose it could happen.
> Because aggregate reports only come in once every 24 hours from most
> places, he's not going to get immediate gratification like he would simply
> by having a few test or seed accounts at the target domain, but maybe he's
> patient. Of course, DMARC isn't the sole arbiter of whether or not the
> message made it to the Inbox and not the Junk or Spam folder, so results
> would be inconclusive at best. His test accounts will tell him much more
> than DMARC reports will tell him.
>
> I can't speak for any mailbox providers, but I suspect that the work of
> updating their reporting tools to handle an exception list and curating
> such a list is more expensive to them than whatever risk might exist in
> generating a DMARC aggregate report for a few spam sending domains. Maybe a
> note in Security Considerations or something? *shrug*
>
>
> --
>
> *Todd Herr* | Sr. Technical Program Manager
> *e:* todd.herr@valimail.com
> *p:* 703.220.4153
>
>
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