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Re: [ietf-smtp] mailing lists are complicated, was Email explained from first principles

2021-05-29 04:58:49
On Fri 28/May/2021 20:18:19 +0200 John Levine wrote:
It appears that Alessandro Vesely  <vesely(_at_)tana(_dot_)it> said:
Mailing lists often do keep DKIM signatures intact. They only alter the rest of the message, but the transformations they do are stylized enough to allow to revert them and verify the original signatures. ...

We've been around this barn a few times before. What you say may seem
true if you have only seen a few lists handled by a single list
package. In reality, I have seen lists add headers and footers, add,
delete, and reorganize MIME parts while changing the MIME boundary
strings, rewrite URLs in message bodies, and flatten HTML bodies into
text. There is no way to list all of the common changes, much less
describe how to reverse them.


There are also lists that gave up making any change in order to not break DMARC. Some other lists cannot afford that, and turn to From: rewriting. If they can manage to restrain from irreversible changes, the original From: can be safely restored.

Reverting From: rewriting is a practical approach which works for cooperating lists and cooperating author domains.


In any event, whatever you might want to do by reviving DKIM signatures is 
already
handled by ARC, so it'd be a lot more productive to encourage ARC adoption than
to invent yet another half-hearted DMARC workaround.


ARC is a completely different thing. It introduces a third party, the sender, which modifies the message header in such a way to induce receivers to accept a message even if it fails DMARC. Semantically, it is very similar to Dave's Use of the Sender Header Field.

ARC is good for global providers who are able to rate intermediate senders.

I see no conflict between these two methods.


Best
Ale
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