Aimed at tracing out the email-virus propagation rules in communication network, this paper extends the traditional epidemiological model (i. e., SEIR) by taking into account the behavior of email users, such as email checking frequency and anti-virus information security policies, and discusses the factors that affect the email-virus propagation in an organization. With the extended SEIR model, namely E-SEIR, three aspects of information security policies (i. e., immunization, information security training,and user recovery support) are investigated in terms of their impacts on the email virus propagation. The results show that the E-SEIR model is suitable to reflect the propagation pattern of email virus, and may also be used in anti-virus policies simulation and evaluation.