Nowadays email clients which support encryption and signature are mostly based on PKI system. The troubles introduced by the certificates bring a lot of inconvenience to users. Identity based encryption (IBE) is an asymmetric cryptographic algorithm that uses a user's unique identity as the public key, so that the troubles of exchanging and distributing public keys are avoided. However, the present standard applications do not support the IBE algorithm. To address this issue, we come up with the pseudo RSA digital certificate technology, which stores an IBE key in the RSA key structure of a certificate, and put forward a scheme of using an IBE plug-in component to implement the IBE functionality for the Outlook and Thunderbird.