In a method and a device for transferring an e-mail by a public key cryptography between an e-mail transmission device and an e-mail reception device, a trigger message to which user authentication data and a public key are added is received from a transmitting side client, and trust is assigned to the public key within the trigger message to be transmitted to a receiving side client when the user authentication data within the trigger message are authenticated. In response thereto, a response message to which user authentication data and a public key are added is received from the receiving side client, and trust is assigned to the public key within the response message to be transmitted to the transmitting side client when the user authentication data within the response message are authenticated.