I'm putting this here, but please add tags/people as appropriate.
I've tried several times to sign up for the public policy list through the policy website — and I've never been taken to the confirmation email. But when I signed up for the public policy listserv through the Wikimedia listserv page, it worked!
@jrbs reports that "I can have a look in the source of the page; looks like it's trying to send something but not actually sending anything. It would probably be best to link directly to the mailman signup page. Right now it's trying to "POST" the information there which I'm not sure is something that mailman can even do."
I know the site was heavily promoted when the blog post about it went live, and I suspect there may have been a lot of people who tried to get updates, and weren't successful.
Right now it doesn't appear to be editable on Wordpress, though it might just be hiding somewhere unobvious.