[Mailman-Users] Newsgroup interface picking up spam

[David Beaumont]

On our members only list how can we prevent the newsgroup interface picking
up posts (spam) from non members?  We have mailman 2.1.8.  I see here 

http://staff.imsa.edu/~ckolar/mailman/mailman-administration-v2.html 

there is an option

"Should newsgroup posts not sent from the list be resent to the list?
Specifies whether or not messages posted by people out there in the world
who are not members of the list should be gated and distributed to list
members. " 

Which would seem to be the answer but we don't have that, is it new in
2.1.9?

Thanks

David