VMS Help MAIL Routines, MAIL$MAILFILE_COMPRESS, Condition Values Returned  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    SS$_NORMAL         Normal successful completion.
    MAIL$_INVITMCOD    The specified item code is invalid.
    MAIL$_INVITMLEN    The specified item length is invalid.
    MAIL$_MISREQITEM   The required item is missing.
    MAIL$_NOTISAM      The message file is not an indexed file.
    RMS$_FNF           The specified file cannot be found.
    RMS$_SHR           The specified file is not shareable.
    SS$_ACCVIO         Access violation.
    SS$_IVDEVNAM       The specified device name is invalid.
    Any condition value returned by LIB$FIND_IMAGE_SYMBOL,
    LIB$RENAME_FILE, $CREATE, $OPEN, $PARSE, and $SEARCH.