This paper has developed a client system to ensure security of email. This system has combined the S/MIME protocol, SMTP protocol and POP3 protocoland realized triple-DES ,RSA and SHA-1 algorithms to process the MIME body .

• 本文基于S/MIME协议,采用了三重DES加密算法、 RSA算法和SHA-1散列算法,并综合了SMTP协议和POP3协议,开发了一个安全电子邮件客户端系统。