Hi, Stefan! Hi, all!
lately, I receive lots of junk mail seemingly sent via the gpc mailing list. One example of the many is appended. If there is a whole in the list,
There is no "hole"; it just seems as if the list's address were in some spammers' database. The only way to get out would be to change the list's address.
could this be plugged with some sort of spam filter,
There is no spam filter that is 100% secure not to trigger on some wanted email. The best possibilities I am aware of are the Teergrube by Lutz Donnerhacke (see http://www.iks-jena.de/mitarb/lutz/usenet/teergrube.html), the Open Relay Behaviour-modification System (see http://www.orbs.org) and the Realtime Blackhole List (RBL) by Paul Vixie (see http://maps.vix.com).
or some mechanism that allows only properly subscribed users to mail via the list?
That would be inappropriate because it would also exclude those who are not (yet?) subscribed to the list but ask for help with GNU Pascal. Remember that it may take some significant time from your subscription until you are in the list.
What you *can* do is to send a complaint about each junk mail you get to the appropriate address. Recently I posted some instructions how to do that to this list; mail me if you want a fresh copy.
Peter