RFC 977 says that the fourth field of the "list of valid newsgroups
    associated information" returned must be "either 'y' or 'n'
    indicating whether posting to this newsgroup is allowed ('y') or
    prohibited ('n'). Most implementations simply output the exact
    contents of the transport system's active newsgroup list. For more
    implementations, the fourth field usually has more values that 'y'
    or 'n'.