How to restrict mailman list subscriptions to certain domains?

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http://serverfault.com – Is there any way to restrict a mailman mailing list to only allowing subscriptions from one specific domain? I know how to ban specific email addresses or domains from subscribing, but is there a way to ban all domains that aren't, say, example.com? Or maybe a couple specific domains? We're starting to get hit by subscription attempts to some of our lists from what I'm sure are spammers on botnets1 and it's annoying list owners. Some lists are configured with a subscribe_policy of "Require approval" or "Confirm and approve" because the lists are intended to be only for our local users and it ()