We may wish to consider setting a better default for nonmember_rejection_notice. See some discussion in an upstream bug filed by a user of one of our current redhat.com lists: https://bugs.launchpad.net/mailman/+bug/418728. If we defaulted to something better, perhaps the wording upstream is considering using for mailman-2.2, it might be helpful to list users.
Regarding rebuilding of archives, can't we let the old archives at redhat.com remain instead of redirecting? That way, links in the archives which point to the existing archive will not be broken. We could probably get the redhat.com mailman admins to edit the archive index.html to point to the new archives as well as update "You can get more information about this list" link. This is in /var/lib/mailman/archives/private/<listname>/index.html in a default mailman install on redhat.