The Realization Of Safe Mail User Agent Based On E-mail Protocol

With the development of modern communication technology, email has become the most popular method of communication due to its convenience and shortcut. Meanwhile, a good email user substitution system can provide a friendly interface to make various operation convenient and significantly simplify these operation. Thereinto, the email encryption function guarantees a safe transmission in the network.In this dissertation, first, it simply states the concepts of computer network and the basic principles of TCP/IP protocol, emphasizing on introducing the functions and its realization of diverse protocols related to email; Secondly, it simply introduces network programming under the Windows operation system; Thirdly, it discusses the basic principles of DES encryption algorithm and explains concrete realizing process of DES encryption algorithm in details; It expatiates on the design and realization of email user agent system. Meanwhile, it describes the realization and function of various network communication modules in details.In this dissertation, the email user agent system is realized under the VC2005 Development Platform, based on C/S mode programming. This system concretely realizes functions of sending and receiving emails, sending attachment and email encryption. According to Quoted-Printable coding that the Multipurpose Internet Mail Extension Protocol (MIME) adopts to email letterhead, we adopt BASE64 coding to the attachment. According to Simple Message Transfer Protocol (SMTP), we realize email sending function; According to Multipurpose Internet Mail Extension Protocol (MIME), we realize sending attachment function; According to Post Office Protocol (POP3), we realize email receiving function. The clients utilize DES encryption algorithm to encrypt emails at the sending end and decrypt emails at the receiving end to guarantee the email safe transmission in the network.In this dissertation, it systematically researches into the design process of email user agent system and simply realizes those protocols related to email. This makes us understand these network protocols deeply and acquaint with the communication between clients and servers. In this design, it utilizes DES encryption algorithm to encrypt emails to make us simply understand the encryption process. Therefore, it has a practical meaning to us all.