Re: [dmarc-ietf] ARC vs reject

Michael Thomas <> Sun, 06 December 2020 17:01 UTC

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From: Michael Thomas <>
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Date: Sun, 6 Dec 2020 09:01:04 -0800
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Subject: Re: [dmarc-ietf] ARC vs reject
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On 12/6/20 5:40 AM, Alessandro Vesely wrote:
> On Sun 06/Dec/2020 02:34:45 +0100 Michael Thomas wrote:
>>> 5) The work you and Alessandro have done with reverse transformation 
>>> is more likely to produce a solution for the mailing lists.   The 
>>> lists will continue to do From rewrite, but reverse-transform 
>>> recipients can validate the true source of the message and restore 
>>> the From if desired.
>> I'm starting to get a little more serious about my quip that the MLM 
>> can insert a sed script in a header to unmangle the message since it 
>> knows what transforms it has done, unlike the receiving MTA trying to 
>> guess the common transformations.
> But then the receiving MTA will have to guess whether the sed script 
> considerably alters the intended meaning of the message. For example, 
> does it change a bank account number?
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.