Re: [dmarc-ietf] Reversing modifications from mailing lists

[Alessandro Vesely <[e-mail]>]

On Mon 29/Nov/2021 04:03:57 +0100 John Levine wrote:
> It appears that  <[e-mail]> said:
>>> It appears that Wei Chuang  <[e-mail]> said:
>>>> If the RFC2045 canonical representation at the final destination can be the
>>>> same as the canonical representation at the original sender, ...
>>
>>> When we were working on DKIM canonicalization we had lengthy discussions about
>>> what to do about MIME and we decided not to even try.
>>
>>A mistake IMO.
> 
> This was part of the discussion about what sort of body modifications to
> allow. We ended up with optionally ignoring white space changes, and l= to
> ignore added text. My impression is that neither is useful. Very few
> messages pass with relaxed canonicalization that don't also pass strict.

Using relaxed rather than strict is quite different between header and body. 
It is fairly frequent to find reflowed headers, especially with MLM handling, 
while bodies remain mostly untouched, except for CR additions and removals.

Of course, X-MIME-Autoconverted rewrite bodies beyond strict/ relaxed range. 
(That's the original mistake.)


> The goal of l= was to allow mailing lists to add footers, but as we've seen
> in this discussion, if a list adds a footer it's likely to make other
> changes too.

It'd be enough to add the subject tag on new messages to address the other 
changes.  Using l= works well with a wide range of mailing lists.  However, it 
only works with plain text.


Best
Ale
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