It would be convenient for a non-subscribers-can-post group to be able to prevent known spammers from posting repeatedly. My guess is that banning an address in such a group does not accomplish that(?). If so, my suggestion is to disallow posts from banned addresses even in a group set to non-subscribers can post.
-- J
Messages are the sole opinion of the author, especially the fishy ones.
I wish I could shut up, but I can't, and I won't. - Desmond Tutu