Re: [dmarc-ietf] ARC vs reject

Alessandro Vesely <vesely@tana.it> Mon, 07 December 2020 09:35 UTC

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From: Alessandro Vesely <vesely@tana.it>
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Date: Mon, 7 Dec 2020 10:35:26 +0100
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Subject: Re: [dmarc-ietf] ARC vs reject
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On Sun 06/Dec/2020 19:47:24 +0100 Michael Thomas wrote:
> On 12/6/20 10:31 AM, Alessandro Vesely wrote:
>> On Sun 06/Dec/2020 18:01:04 +0100 Michael Thomas wrote:
>>>
>>> This actually highlights why my observation is correct. If the intermediary 
>>> showed how to reverse their changes perfectly to be able to validate the 
>>> original signature, it says nothing about whether those changes to be 
>>> delivered to the recipient are acceptable to the originating domain. for the 
>>> case of a bank sending me sensitive mail, the answer is that it is never ok. 
>>> for somebody working on internet standards working on ietf lists, the answer 
>>> is that it is fine. hence trying to get two states of the one "reject" is 
>>> insufficient.
>>
>> For MLM transformations, this choice can be done by tuning DKIM signatures.  
>> A bank can choose to sign Sender: field (or lack thereof), or any other 
>> fields that a MLM has to change, and possibly use simple canonicalization.  
>> In that conditions, transformation reversion won't work.  It isn't a distinct 
>> DMARC state, formally. Yet, tuning DKIM signatures allows to harden or weaken 
>> the given DMARC state.
>>
> It seems a lot simpler for the originating domain to just be explicit about how 
> they feel about transformations by intermediaries. It's not like another short 
> ascii string is going to break the bank.


A stated policy is certainly more explicit about the intent.  However, it is 
subject to receivers interpretation and I-dont-care syndrome.


Best
Ale
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