PS: Clearly, the interaction between ISP and a mailing list could be
disturbed, sometimes it's the bad of the mailing list and sometimes
it's the bad of the IPS. Black hole lists, rejected emails, odd
filters. If the disturbance reaches an annoying traffic producing
level, then Debian list unsubscribes, while mailman lists, such as LAU
usually disable mail delivery. IOW the ISP never unsubscribe users from
mailing lists, the lists automagically unsubscribe their members.