> I'm tring to modify a list that the owner wants fully moderated but
> to reject posts from non-listmembers.

put this in the header:

Send= Private

then only subscribers can post.

see the listowner manual:

2.12.6 Controlling who may post mail to the list

    "For  a list  that  does  not allow  non-subscribers  to  post,
    set  Send=Private."



  ...Cleo  [log in to unmask]