[COFF] OT: Any DKIM People Out There?

[Warren Toomey via COFF]

Hi all, I've had a question/issue raised with DKIM on the TUHS/COFF mailing
lists from a subscriber. I'm running Mailman3 and I'm a DKIM newbie. They
say:

    Why have all mails from the tuhs mailing list, except those
    from a real tuhs.org domain (basically only yours), an invalid
    DKIM? Background, my mail provider will switch its DMARC policy from
    "none" to  "quarantine" and then to "reject" - which will result first
    in tuhs-mails being marked as "spam" and later being rejected. Other
    mailing lists I receive, switch the sender domain to the list domain
    itself. This results in a correct DKIM. Wouldn't this be possible
    for the tuhs-list too?

He gives, as examples:

    Maillist mails from senders "via TUHS <tuhs at tuhs.org>" pass DMARC
    (e.g. Cameron Míċeál Tyre via TUHS <tuhs at tuhs.org>).
    Maillist mails from senders without the "via TUHS" part fail DMARC
    (e.g. Blake McBride <blake.... at gmail.com>). 

I'd be very happy to have someone/some people review my mailman3, postfix
and rspamd configuration and suggest changes.

Many thanks in advance,
	Warren

P.S. Anybody know of an Internet server still running continuously from
before May 1991 (esp. being maintaned by the same owner)? viz:
https://minnie.tuhs.org/minannounce.txt