set "Should Mailman filter the content of list traffic according to the settings below?" to yes
add these to pass_mime_types: ----------------------------- multipart/mixed multipart/alternative text/plain
set "Should Mailman convert text/html parts to plain text? This conversion happens after MIME attachments have been stripped." to yes.
set "Action to take when a message matches the content filtering rules." to "Forward to List Owner" and the owner of LBO will receive emails that could not be converted or do not pass the test. or choose Reject to let the submitter know they sent in wrong format.
Les Schaffer