/sys$common/syshlp/helplib.hlb EXCHANGE, DISMOUNT, Qualifiers, /MESSAGE  *Conan The Librarian (sorry for the slow response - running on an old VAX)

       /MESSAGE
       /NOMESSAGE

    Controls whether or not EXCHANGE displays a message that the
    volume was dismounted. The default is determined by the /MESSAGE
    qualifier on the EXCHANGE command when EXCHANGE was activated.