Abstract. E-mail is a kind of communication mode which provides information exchange through electronic means. Nowadays, more and more enterprise units cooperate with e-mail to break the limitation of time and domain, and realize office automation, which greatly improves work efficiency. It can be said that e-mail has become an indispensable part of people's life. This paper first describes the development background and system development platform of e-mail client application, and introduces the technology used in the system development. In the analysis phase of the system, the structure of e-mail and the format of e-mail text are analyzed, the working principle of e-mail is mastered, and the SMTP and POP3 protocols are deeply studied. In the design and implementation of the system, determine the system development ideas and development environment. Finally, the detailed design and implementation of the module in the system are given, and the key source code involved in the system module is analyzed in detail.