> Secondly, it seems that listserv will only check the From: field in the
> SMTP envelope on any message for subscriber validation. This makes it
> relatively easy to masquerade an address on any mailer program that will
> allow you to manipulate the header, allowing actions to be taken on
> someone else subscription regardless of whether the list is open or
> closed. It is not secure enough.

Put this in your header:

Send= Private,Confirm

This requires each poster to confirm (via the "OK" mechanism) that the posting
actually came from them.