There's an active spamassassin from what I can see sometimes that filters some of them, but it doesn't always work. The owners of the mailing lists can and will be spammed since their address is shown at the subscription page :) Just don't allow non-members to post on the mailing list, the mailing list software sends (I think by default) a message that they are blocked and they have to sign up to send a mail :)
-- loco-contacts mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/loco-contacts
