Re: [dmarc-ietf] Proposed text for p=reject and indirect mail flows

[Mark Alley <[e-mail]>]

I have a question for the group; I have read RFC7960, but I feel my 
question merits reiteration for those of us on this list (like me) that 
may have differing opinions on this topic from experience as a consumer 
of the standard, and having worked with many of these "general purpose" 
domains at p=reject.

The concern with interoperability with p=reject is that if, 
hypothetically, every domain on the internet were to go to p=reject 
right now, the damage would be tangible because many indirect and 
"non-DMARC described" mail flows would be prevented from delivery? 
(non-5322.FROM munging mail lists, some non-descript mail relays, a 
random mailbox forwarding, a non-DKIM preserving forwarding mail 
service, non-DKIM signed forwarded mail flows, etc. etc.) Is this a 
correct assessment behind the reasoning for the "MUST NOT" language?

I am concerned that others may see this language and perceive it as 
weakening the value of DMARC, or that DMARC should not be implemented at 
all, when there is a proven track record of many <general purpose> 
domains that have implemented strict policies to great effect in 
securing their domains without major issues.

-----

Separately, from a "general purpose" domain owners perspective, I share 
Alex's thoughts. Having worked with many (extremely high volume) 
non-transactional domains at p=reject, the noticeable issues caused from 
p=reject has been negligible to these organizations.

Many of the mitigations from RFC7960 already apply to the traffic that 
would have otherwise been impacted by what would normally be considered 
an interoperability issue otherwise. That is not to say there is not 
/any/ impact from its implementation, but from an organizational 
standpoint, all the important messages are still delivered. There have 
been outliers, of course, but they are dealt with by the organizations 
on a case-by-case basis, which, to date, have been less than a handful.

- Mark Alley


On 3/29/2023 3:59 PM, Scott Kitterman wrote:
> Would you feel any better if the MUST NOT was followed by 'to preserve interoperability '?  That's implicitly there and I believe technically correct.  If you value other properties of the system higher than interoperability, then the advice may not apply, which is fine.
>
> Scott K
>
> On March 29, 2023 3:32:10 PM UTC, "Brotman, Alex"<Alex_Brotman=[e-mail]>  wrote:
>> I’m just not sure how we determine what is high-value.
>>
>> comcast.com: p=reject
>> comcast.net: p=none
>> xfinity.com: p=quarantine
>>
>> The top one is corporate, middle is consumer, bottom is consumer (but not actually used) & customer comms (sub-domains).  They’re all used in various ways for internal messaging.  Should I tell our corporate admins that they need to no longer publish p=reject?  They’re violating the RFC by doing so?  There are very few consumer-oriented messages that originate from comcast.com.  Are we doing it right?  It makes things a little harder when one of our employees wants to use a mailing list.  But that still feels like the right thing to do.
>>
>> If it’s not obvious, I’m having a hard time with “MUST NOT”, and dictating to domain owners what is in their best interests, regardless of our perceived value of their domain.
>>
>> --
>> Alex Brotman
>> Sr. Engineer, Anti-Abuse & Messaging Policy
>> Comcast
>>
>> From: dmarc<[e-mail]>  On Behalf Of Barry Leiba
>> Sent: Wednesday, March 29, 2023 10:15 AM
>> To: Todd Herr<todd.herr=[e-mail]>
>> Cc:[e-mail]
>> Subject: Re: [dmarc-ietf] Proposed text for p=reject and indirect mail flows
>>
>> I'm very much against text such as this, as I think it encourages deployments that are contrary to interoperability and to the intent of p=reject.
>>
>> I contend that p=reject (as with the similar construct in the older ADSP) was intended for high-value domains and transactional mail, and that it was never intended for use in domains where general users send general email.
>>
>> I stand by the MUST NOT that I proposed.
>>
>> Barry
>>
>>
>> On Wed, Mar 29, 2023 at 10:33 PM Todd Herr <todd.herr=[e-mail]<mailto:[e-mail]>> wrote:
>> On Tue, Mar 28, 2023 at 9:06 PM Pete Resnick <[e-mail]<mailto:[e-mail]>> wrote:
>>
>> If you agree that interoperability is increased, then I'd suggest that you actually do agree that the proposed text is appropriate.
>>
>>
>> I don't know that I agree that interoperability is increased...
>>
>> I'm having trouble squaring proposed language that says "Domain owners MUST NOT publish p=reject because it breaks interoperability" with the following language from section 5.8:
>>
>>
>> Mail Receivers **MAY** choose to accept email that fails the DMARC
>>
>> mechanism check even if the published Domain Owner Assessment Policy
>>
>> is "reject". In particular, because of the considerations discussed
>>
>> in [@!RFC7960], it is important that Mail Receivers **SHOULD NOT** reject
>>
>> messages solely because of a published policy of "reject", but that
>>
>> they apply other knowledge and analysis to avoid situations such as
>>
>> rejection of legitimate messages sent in ways that DMARC cannot
>> describe, harm to the operation of mailing lists, and similar.
>>
>> It seems inconsistent to state with certainty that authorized mail will be rejected due to authentication breakage when there is no requirement that a reject policy be honored (and we have plenty of evidence that Mail Receivers are following the 'SHOULD NOT reject messages' guidance).
>>
>> Language that would be more consistent in guidance to the domain owners might look something like this:
>>
>> After careful analysis of the aggregate report data as described in section 5.5.5
>> (Collect and Analyze Reports), Domain Owners **MAY** choose to change their
>> policy from 'none' to 'quarantine' or 'reject'. If, in the Domain Owner's judgement,
>> unauthorized and deceptive use of its domain name in the RFC5322.From field puts
>> at risk the trust it has built with its recipients, then it is **RECOMMENDED** that
>> the Domain Owner make use of the p and/or sp tags to set policy to 'quarantine' or
>> 'reject' for those streams most at risk of loss of trust.
>>
>> If going that route, probably want to consider expanding on 5.5.5, too; I need to think about it some more.
>>
>> --
>> Todd Herr | Technical Director, Standards and Ecosystem
>> e:[e-mail]<mailto:[e-mail]>
>> m: 703.220.4153
>>
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