I’ve upgraded the Mailman version on mail.gnome.org to 2.1.10. In this version I redid the post-only patch. Basically, if the default action for new subscribers is to moderate them (done on e.g. metacity-devel-list), then members subscribed to post-only won’t be automatically accepted. In 2.1.10 Mailman supports something like post-only by default (see NEWS). I found it easier to patch this logic in than to change existing lists and to ensure new lists would get the post-only setting as well.
If you see any problems, please email gnome-sysadmin. Note that yesterdays email backlog wasn’t caused by the Mailman upgrade. I waited until it cleared.