本文分析了 Email系统安全问题产生的原因及现有对策的不足 ,在此基础上 ,提出多级安全机制和智能预警机制 ,以提高 Email系统的安全性 ,并提出了能有效解决线路分析攻击的方案。根据上述思想 ,设计并实现了一个新的安全 Email系统—Sec Mail,使之适用于有较高安全要求的 Intranet环境。 This paper analyzes the causes of the Email system security problems and the shortcomings of the existing strategies. Based on this, we propose a multi-level security mechanism and an intelligent early warning mechanism to improve the security of the Email system. Program. According to the above thought, a new secure email system -Sec Mail is designed and implemented, which makes it suitable for Intranet environment with high security requirements.