VMS Help EXCHANGE, MOUNT, Qualifiers, /FOREIGN  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    Indicates that the volume is not in the standard format used by
    the OpenVMS operating system; that is, a magnetic tape volume
    is not in the standard ANSI format, or a disk volume is not in
    Files-11 format. The EXCHANGE command MOUNT mounts only foreign
    volumes. The /FOREIGN qualifier is the default. You must use the
    DCL command MOUNT to mount OpenVMS volumes.

    The default protection applied to foreign volumes is RWLP (Read,
    Write, Logical I/O, Physical I/O) for the system and owner. If
    you mount a volume currently in Files-11 format with the /FOREIGN
    qualifier, you must have the user privilege to override volume
    protection (VOLPRO), or your UIC must match the UIC on the
    volume.