I may include more info than you really want to know. Here is the gist of the complaint:
"For a while now, my e-mail for this list (but not other lists) just shows "To RADG" from "RADG" with a "CC" showing the actual sender's address. That becomes a PITA when I need to find a post by a particular person, because the e-mail list does not show the CCs in the list, so I need to open each one to see who actually sent it."
This subscriber is not very savvy about email, and doesn't seem to understand fully when I tell him how it works, so if I start talking about headers, that's a PITA, too. He claims:
"RADG is the only list that is afflicted by this, out of 21 that include groups.io, yahoo, google, Lyris, and probably a few I don't recall."
Because some other members, including me, have had problems with unexpected entries in both From and To lines, I suspect that Mailman 3 does the DMARC enough differently than other lists and forums to cause conflicts with the way the MUAs try to help the user autocomplete an address. Most of those problems go away if they put an association of RADG (Risk Analysis Discussion Group) with radg@lists.radg.us in their address book. We chose the "use your own URL" option. The actual server address is deu.mailmanlists.eu; I don't know whether their customization of the MM3 installation might cause some of the problem.
My understanding is that all of the recent posts are missing the poster's name, after behaving as expected for some time. Something must have changed, but what is baffling me. If you have any further ideas, fine, but don't waste a lot of time on this.
Steve