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Mailing-list DMARC changes?

Posted by MichaelAtOz on Oct 22, 2019; 3:23am
URL: https://support.nabble.com/Mailing-list-DMARC-changes-tp7604436.html

[prologue: If you happen to look at the mailing-list/posts disregard anything since 10 Oct, as I was trying various DMARC settings from then]

When SPF & DMARC was introduced Mailing-lists had difficulties.

Enforcement of this was added by Yahoo years ago, and other domains they control such as @aol.

Mailing-list software provided work-arounds, Gnome Mailman, has an option which 'munges' the From header so it matched the domain, only for affected user domains.
For http://forum.openscad.org the list is discuss@lists.openscad.org,
so the munge is e.g. From: <joe@example.com>  changes to From: joe via discuss<discuss@lists.openscad.org> 

I suspect something in Nabble changed recently.
Originally such yahoo mails got on the mailing-list but never made it to the forum.
Now, since June 10, they (munged emails from multiple users) are posted to the forum against an unregistered user 'discuss@lists.openscad.org'
See http://forum.openscad.org/template/NamlServlet.jtp?macro=user_nodes&user=1513 
(note this forum is set to restrict posts to registered users)

Was this a Nabble change?

Also note that the mailing-list munge puts the original email address in the Cc field.
So I'm wondering if the 'incoming email' 'post' process could check if 'from' == the mailing-list address, check the (first/only?) Cc email-address, and if it matches a Nabble user, then post against that user?

Or is there some other DMARC solution?

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or, this thought just popped-up,
Why does Nabble get the munged email?
Nabble is subscribed to the mailing-list, as lists+s<scrambled> at n5.nabble.com
Mailman should only munge messages DESTINED *TO* A DMARC RESTRICTED DOMAIN.
As Nabble is getting munged emails that means it has implemented SPF/DMARC???