[Mailman-Users] Restrict posting for members only while using NNTP gateway

[Michael Stucki]

I am running a mailman installation that uses NNTP synchronisation.
Due to an increasing amount of spam mails, I would like to restrict posting
to the lists for members only.

My problem is that this won't work well since I also use NNTP
synchronisation. Most users who post there are not subscribed to the
according lists, so their postings would not be accepted anymore.

In my list setup, I can specify a list of non-member addresses whose
postings were automatically accepted. What I need is something very
similar, but instead of listing addresses, I'd like to check for a specific
header information (e.g. Received: from <nntp-server> ...)

Anybody else who ever had this problem? How can I solve it?

Thanks for your comments.
- michael