Recently

Sun et al. (

2005

2005

) highlighted the essential property of perfect forward secrecy (PFS) for e-mail protocols when a higher security level is desirable. Furthermore

Sun et al. (

2005

2005

)’s protocols take only a single e-mail server into account. Actually

it is much more common that the sender and the recipient register at different e-mail servers. Compared to existing protocols

the protocol proposed in this paper takes into account the scenario that the sender and the recipient register at different servers. The proposed protocol is skillfully designed to achieve PFS and end-to-end security as well as to satisfy the requirements of confidentiality

origin

integrity and easy key management. The comparison in terms of functionality and computational efficiency demonstrates the superiority of the present scheme.