/sys$common/syshlp/helplib.hlb MAIL Command, Parameters  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 filespec

    Specifies an optional file containing message text to be sent to
    the specified users. If you omit the file type, the default file
    type is TXT. The recipient-name parameter is required with the
    filespec parameter.

    If you omit the filespec parameter, MAIL is invoked to process
    MAIL commands interactively.

    No wild card characters are allowed in the file specification.

 recipient-name

    Specifies one or more users to receive the message. If the
    filespec parameter is specified, this parameter is required. A
    recipient-name is the name that the user uses to log in. If any
    user is on a remote node, you should precede that recipient-name
    parameter with the name of the remote node followed by two colons
    (::).

    As an alternative to listing the user names, you can specify a
    distribution list file containing user names. Simply precede
    the distribution list file specification with an at sign (@)
    and enclose this construction in quotation marks ("). The file
    you specify should contain the user names, entered one per line,
    denoting any remote nodes as described above. If you omit the
    file type, the default file type is DIS. No wild card characters
    are allowed in the distribution list file specification.