I am a big fan of procmail, which is a mail-filtering program,
and propose another method of spam filtering. It is much less
complicated than it sounds.
1. change the list alias so that instead of sending mail to resend,
it goes to a user account, which could even be the list-owner's
2. set up procmail on that account so that it takes mail addressed
to the list and passes it through whatever filters you want.
With procmail, it's easy to check the sender's address against
a file of addresses you want to reject, and you can have procmail
send them a canned refusal. All normal mail to that account passes
through the user. You could even set up a single account that
filters mail for ALL your mj lists.
3. If the mail passes all the filters, it gets sent to the real
list alias (to resend).
This strategy could be used for a lot of different things like
catching articles about sensitive topics, stopping flames, etc.
because procmail can scan the whole email to see if it contains
key words and so on.
Procmail is shareware; you can get it from ftp.informatik.rwth-aachen.de