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 would be nice to minimize the annoyance of the list owners by automatically rejecting subscriptions from outside email addresses that won't be allowed to subscribe by the list owner anyways.
We can't simply restrict access to the local networks because we have lists intended for a worldwide audience and some of our "local" users can be anywhere.
1 One email address subscribes to a couple dozen unrelated lists from different IPs over a few hours; then the next day another round with a new email address and different IPs. In a few cases list owner has emailed them a question about why they were signing up for the list and received no reply.