This is the closest there is unless you change folder access to Read Only which would also prevent posting. Even still they might be able to edit and delete messages already posted — I haven't checked.
Under Controls - Main Settings:
Do you want to let your members edit their messages? This is a helpful tool for cleaning up typos and spelling errors. All edits are noted in an audit trail at the bottom of the message.
My guess is that you cannot prevent people from deleting their own messages, much like forum managers retain the ability to edit or delete anyone's messages.
Edited 6/16/2002 11:19:55 PM ET by EdGlaze