Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821, August 1982. Partridge, C., "Mail routing and the domain system", STD 10, RFC 974, January 1986. Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. Crocker, "SMTP Service Extensions", STD 10, RFC 1869, November 1995. Klensin, J., Freed, N., and K. Moore, "SMTP Service Extension for Message Size Declaration", STD 10, RFC 1870, November 1995.