https://lists.wikimedia.org/mailman/listinfo/offline-l only lists inactive erik at wikimedia.org as list admin/moderator.
That means that any emails sent by non-subscribers to that list do not get through, as simply nobody can approve them.

@Kelson, @StephaneKiwix: You seem to be the most active folks lately on that list.
Could you imagine going through the moderation queue in Mailman, and have some basic experience with Mailman?
Or do you have someone else in mind?

If not, I'd volunteer to become the admin/moderator of that list.