Re: Not usable email content encoding

[Mark Wielaard <mark@klomp.org>]

Hi,

On Tue, 2020-04-07 at 11:53 +0200, Florian Weimer via Overseers wrote:
> Gmail can drop mail for any reason.  It's totally opaque, so it's a
> poor benchmark for any mailing list configuration changes because it's
> very hard to tell if a particular change is effective or not.
> 
> Many mailing lists have *not* made such changes and continue to work
> just fine in the face of restrictive DMARC sender policies and
> enforcement at the recipient.
> 
> In general, mail drop rates due to DMARC seem to increase in these two
> cases if the original From: header is preserved:
> 
> * The sender (i.e., the domain mentioned in the From: header)
>   publishes a restrictive DMARC policy and the mailing list strips the
>   DKIM signature.
> 
> * The sender signs parts of the message that the mailing list alters,
>   and the mailing list does not strip the DKIM signature.
> 
> If neither scenario applies, it's safe to pass through the message
> without munging.  The mailing list software can detect this and
> restricting the From: header munging to those cases.
> 
> I doubt Mailman 2.x can do this, so it is simply a poor choice as
> mailing list software at this point.

Earlier versions of Mainman2 had some issues which might accidentally
change some headers. But the latest fixes make this possible. It is how
the FSF handles DMARC for various GNU mailinglists (by NOT modifying
the headers and body and passing through the DKIM signatures):
https://lists.gnu.org/archive/html/savannah-hackers-public/2019-06/msg00018.html

Cheers,

Mark