[1]  Crocker, D., "Standard for the Format of ARPA Internet Text
        Messages", RFC-822, Department of Electrical Engineering,
        University of Delaware, August, 1982.

   [2]  Horton, M., "Standard for Interchange of USENET Messages",
        RFC-850, USENET Project, June, 1983.

   [3]  Postel, J., "Transmission Control Protocol- DARPA Internet
        Program Protocol Specification", RFC-793, USC/Information
        Sciences Institute, September, 1981.

   [4]  Postel, J., "Simple Mail Transfer Protocol", RFC-821,
        USC/Information Sciences Institute, August, 1982.