DKIM fails depending on Content-Transfer-Encoding

fi at igh.de fi at igh.de
Wed Sep 6 14:28:46 UTC 2023


Dear Jan, 

On 2023-09-06 15:25, Jan Eden via Mutt-users wrote:
> On 2023-09-06 13:33, fi at igh.de wrote:
> 
> > Dear Mutt Users
> > 
> > recently I experienced DKIM fails that depend on the
> > Content-Transfer-Encoding of messages text part.
> > 
> > Being a german I use to write my messages in german with UTF-8
> > encoding. I prefer plain text. My e-mails are DKIM signed. I have
> > checked DKIM to be set up correctly twice.
> > 
> > By default Mutt does 8bit encoding for text/plain. Now I found that
> > several (most) of the recipient systems fail to check DKIM.
> > 
> > If I force Mutt to change the encoding from 8bit to 7bit, base64, or
> > quoted-printable (using ^E in the compose menu), the DKIM checks
> > succeed. 
> > 
> > Can I force Mutt to use quoted-printable or base64 by default for
> > encoding of plain text?
> 
> In my experience, mutt chooses the simplest encoding required for each
> message, and it is usually better not to intervene.

that has been my opinion too. But after several tests I found, that
DKIM fails dependent on that very encoding. So now I am convinced,
that Mutt's decision is not the best and I am looking for a
configuration option to fix that.

> > Does anyone have similar experiences? Is there an explanation for this? 
> > May there be any interference with the MTA? 
> 
> At what point do you apply the DKIM signature? If the DKIM signature is
> calculated for the complete message (as created by mutt), there should
> be no mismatch/DKIM failure.

Mutt sends the messages to my MTA and as usual the DKIM signature is
then created by that MTA via Milter (OpenDKIM). And that works as a
charm as long as the plain text is plain ASCII (no UTF-8). It even
works perfectly if the subject contains any non-ASCII characters. Also
names of attachements may contain those characters.  As soon as there
is only one non-ASCII character in the plain text message, Mutt choses
8bit and DKIM fails.


BTW.: I have fiddled with evolution - it seems that there exists a
      similar problem. But I cannot force it to chose another
      encoding. Again: mutt sucks less :-)



Best Regards

Torsten 


-- 
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Torsten Finke
fi at igh.de
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