[Mailman-Users] Auto discard non-members messages

[Daevid Vincent]

I'm starting to see a lot of spam sent to my two lists. Both are members
only. 

I'd like mailman to automatically discard any messages sent to the list from
non-members. However, I would like to accept (and send to me/admin) any
subscribe request messages (otherwise, how would I get new members ;-)

Can someone tell me how to do this?