> Would it not be possible to stop the spam on this list by setting
> majordomo to reject posts from any address which is not in the list of
> addresses subscribed? Wherever this spam is coming from, it is almost
> certainly not from an address signed up to the list. And if it is, that
> address could be deleted from the subscription list.
Doesn't help. I manage 5 mailing lists, most of which have this setting, and they get no less spam than the others. Spammers are crafty buggers--they won't let simple countermeasures get in their way. They just use automated software that creates bogus send addresses, subscribes them to the list, sends mail, then removes any trace that the address ever existed so there's no one to complain to.
This setting does, however, make it tricky for folks like me who get on the net from several different access points to send mail to the list from some of them (my postings often come from "firstname.lastname@example.org" even though my real address is "email@example.com"). That's a minor annoyance, and I (and others) can work around it, but it's an example of how security can get in the way of legitimate use.
Spammers are scum. I don't mean to imply that they should be simply tolerated. Reasonable countermeasures can be done and are being done. I'm just saying that trying to prevent 100% is a bit beyond reasonable, so being annoyed by the occasional one that slips through the cracks is pointless.