After turning up few results by searching the archives, thought

I'd ask here, as I'm sure umpteen others have run across the same thing. I'm unable to locate any options which would cause mailman to immediately discard any message not sent from someone already on the list. A few of my lists get an inordinately large amount of spam, and they'd love to not have to discard all of them every day or 2. Any ideas or help would be much appreciated. Thanks in advance for your time.

David