DKIM fails depending on Content-Transfer-Encoding

Nuno Silva nunojsilva at ist.utl.pt
Thu Sep 7 07:10:24 UTC 2023


On 2023-09-07, raf via Mutt-users wrote:

> On Wed, Sep 06, 2023 at 01:33:30PM +0200, 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?
>> 
>> Does anyone have similar experiences? Is there an explanation for this? 
>> May there be any interference with the MTA? 
>> 
>> Interestingly DKIM checks do not fail if I use non-ASCII characters in
>> the subject. Also attachements do not cause DKIM to fail.
>> 
>> Best Regards
>> 
>> T. Finke
>> 
>> -- 
>> ------------------------------------------------------------------------
>> T. Finke
>> fi at igh.de
>> ------------------------------------------------------------------------
>
> Hi, This has come up recently in the Postfix mailing list.
> MTAs can convert 8bit messages when sending to another MTA
> that doesn't advertise that it can accept 8bit. If the DKIM
> signing happens before the conversion, then subsequent DKIM
> checks will fail. Work is being done in Postfix to address
> this. I don't know about other MTAs. It seems unlikely that
> there are any MTAs that can't accept 8bit messages, but perhaps
> there are some that are misconfigured and don't advertise the
> fact to other MTAs.

Has AOL/Yahoo/Verizon/...'s server software been finally fixed from its
eternal dance between two different failure modes? (Either replacing
non-ascii with ? or messing up the encoding); I think it also
misadvertised 8-bit support to MUAs...

But maybe that really just affects client connections and does not
damage messages received from other servers?

-- 
Nuno Silva



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