3RFC792, Internet Control Message Protocol, http:∥www.faqs.org/rfcs/ffc792.html.
4RFC793,Transmission Control Protocol,http:∥www.faqs.org/ffcs/rfc793.html.
5RFC821, Simple Mail Transfer Protocol, http:∥www.faqs.org/rfcs/rfc821.html.
6RFC822, Standard for the Format of ARPA Internet Text Messages, http:∥www.faqs.org/rfcs/rfc822.html.
7RFC1521 ,MIME (Multipurpose Internet Mail Extensions)Part One:Mechanisms for Specifying and Describing the Format of Internet Message Bodies, http:∥www.faqs.org/rfcs/ffc1521.html.