[COFF] OT: Any DKIM People Out There?

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