Use the HOLD command to mark as held any messages which should
    temporarily be placed on "hold". PMDF will not attempt to deliver
    any messages which are marked as held. To resume processing of a
    held message, use the RELEASE command. Messages which have been
    held can be listed with the DIRECTORY/HELD command.

    The messages to be held 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.