It is possible to configure a moderated mailing list (Security tab - Server Moderated) without setting an owner. If this happens and messages have been sent to the list you can re-authorize the messages by following these steps,
Assign an owner to the mailing list (Mailing List tab).
Navigate to the mailing list directory, default is,
Move the message files (.tmp) from the list folder to the owners inbox.
Have the owner log on to Webmail and redirect each message back to the list. The owner will then get an approval message from the list.