Design And Implementation Of SMTP E-mail Client And Server

With the explosively growing of the Internet at present, E-mail has become a widely used means in daily communications. The E-mail sytems are composed of clients and servers. According the difference of the platform, the E-mail servers can be divided into two classes, UNIX and Windows. Although servers based on UNIX are open source, it is requested administrators not only master the frame of servers, but also have abundant experiences of programme on UNIX. Among various servers on Windows platforms, most are large commercial softwares. They are too expensive and require high performances of the host. In practice, the E-mail systems are usually developed again. But the existing clients are nor open source, it is defficlut to enhance their capability. So we develop DSPMail which is a pocket E-mail system with the client and server.This paper designs and implements the SMTP client, the SMTP receiver server and the transmitting server of DSPMail system, which transport the mail from the addresser client to the addressee mailbox in the server. The thesis contains the following parts:(1) The communication processing between the client and server is implemented in Winsock API.(2) The commands and responses of SMTP and ESMTP protocols are implemented, which accomplish the transport processing of mails and a LOGIN mechanism authentication.(3) The SMTP client is implemented in C language. The mails contain Media accessories and use GB3212 character-set are sent by using Quoted-Printable and Base64 encoding codes.(4) The easily operational interface of clients with MFC on Windows OS is programmed.(5) The SMTP receiver server is designed an implemented in C language. For restricting spasms, the transfer function is forbidden and the identity of addresser must be authenticated.(6) Mails are distributed in the store-and-forward architecture.(7) In the the transmitting server, the final server's IP address of mail is acquire by DNS query.Finally, the compatibility of the DSPMail system and the capability of the SMTP server are tested. It is revealed that the client and server are both compatible very well with other systems and the SMTP server can parallel deals with several connections simultaneously. The DSPMail system can send, receive and transfer E-mails normally in practice.