由于历史的原因,我们已熟悉的一些信息安全的概念、原理、理论、方法与技术都是在单机的、局部的、孤立的系统环境中形成的。因而一些刚涉足电子邮件系统的人,很难相信电子邮件系统是不安全的。这是因为: 第一,进入电子邮件系统必须使用1～3个密码口令或个人身份证,特别是电子邮件的提供者一再提醒,为了保密、用户不要 For historical reasons, some of the concepts, principles, theories, methods and techniques of information security that we are familiar with are all formed in a single, localized and isolated system environment. As a result, some people who are new to e-mail systems find it hard to believe that e-mail systems are unsafe. This is because: First, enter the e-mail system must use 1 to 3 password password or personal identification card, especially e-mail providers repeatedly reminded, in order to keep the user, do not