VMS Help System Services, $DELMBX, Argument  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 chan

    OpenVMS usage:channel
    type:         word (unsigned)
    access:       read only
    mechanism:    by value
    Number of the channel assigned to the mailbox that is to be
    deleted. The chan argument is a word containing this number.