The list appears to have settings enabled:

  - modify the subject by adding [Nut-upsuser]
  - add a footer

I believe these are controlled by the list administrator, in the same
way as reply_goes_to_list.

Both of these are, in the eyes of DKIM, attacks on the integrity of the
message.

I believe that when mailman is attacking the message :-) due to
configuration, and the address in From publishes a DMARC policy, then it
changes the From: and inserts a Reply-To back to the sender.  Or rather
that there is a setting "when breaking the message and From has a DMARC
policy, forge from".

Here are the headers of a message you recently sent to the list (and not
also to me, so I'm seeing the list headers):

  From: Charles Lepple via Nut-upsuser <[email protected]>
  Subject: Re: [Nut-upsuser] Keeping the traffis on or off the list ?
  To: Jim Klimov <[email protected]>
  Cc: Charles Lepple <[email protected]>, nut-upsuser Mailing List 
<[email protected]>
  Date: Sat, 17 Feb 2024 11:09:20 -0500 (43 minutes, 27 seconds ago)
  Reply-To: nut-upsuser Mailing List <[email protected]>

As you can see the From: is forged.

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