本文介绍了电子邮件系统的工作原理及相关协议，并基于这些协议设计和开发了一个实用的邮件收发系统。用户运行软件后可以进行基本操作，邮件管理（邮件发送和邮件接收），用户管理（查询邮件和修改，查询、删除用户），用户可以发送或接收一个或多个带附件的邮件，也可以使用不同的SMTP或POP3服务器。-This paper introduces the principle and protocols of E-mail, which designs and develops an E-mail system based on those protocols. After have logged on the system successful, user can do basic operations-mail management, user management. You can send or receive an E-mail with attachments. Besides, you can also use a different SMTP or POP3 server.