Queued messages may be returned to their originator with the
    RETURN command. The messages to be returned are specified by
    their message identification numbers shown by the most recent
    DIRECTORY command. That number appears in the leftmost column of
    the DIRECTORY command listing. Ambiguous message numbers must be
    qualified by the proper channel name with the /CHANNEL qualifier.

    The returned message is in two parts. The first part explains the
    reason why the message is being returned; the text of the reason
    is contained in the file RETURN_BOUNCED.TXT file located in the
    PMDF language-specific directory. The second part of the returned
    message contains the original message itself.