A common goal is to filter incoming messages, perhaps sending an
    automatic response, forwarding the messages to another account,
    or automatically rejecting or discarding some based upon material
    in the messages' headers or bodies. One way to do this is via the
    DELIVER facility.

    If your messages are delivered to the native message store (VMS
    MAIL mailbox) or to a PMDF popstore or PMDF MessageStore account,
    your system administrators may have chosen to enable another
    option: PMDF message filtering. If your system administrators
    have chosen to enable it, PMDF provides a web-based interface
    through which you can specify a vacation notice, specify a
    forwarding address, and construct and manage your own message
    screening rules. These are collectively known as mailbox
    filters.