About half of the messages in this thread ended up in my spam folder (I use gmail as my mailbox with a custom domain).
From looking at the message headers, I noticed what all the messages flagged as spam seem to have in common: dkim signatures. The dkim signatures are all failing because the body of the message is being altered with the footer message that mailman appends. That was obviously also happening with the old list, but it's reputation likely prevented that specific issue from being considered as highly as it is with this new listserv.
I also noticed that neither listserv domain has spf records published. If a proper spf record can be published, and new messages start passing spf checks, perhaps the dkim failures won't weigh as heavily anymore???
I think the only way to prevent the dkim signatures from failing in the first place is to either replace the email address in the "From: " header, or to prevent modification of the message body by disabling the footer insertion.