Abstract: In a process for transmitting an electronic message that contains protected and unprotected content, the authenticity of the header elements HE is ensured by obtaining a subsequent authenticity verification of the sender. For this purpose, a checking device which is inserted into the transmission network transforms the header elements of the original message into a new message whose contents are protected by known encryption methods. The new message is sent back to the sender which decrypts it and checks the header elements. If the sender verifies the authenticity of the transmitted data, the header elements on which the original message is based are also considered to be verified. According to the invention, the sender who sends the message, and is later requested to verify its authenticity, may be the mail server (Message Transfer Agent “MTA”) as well as the client of the MTA (and thus, the author of the message, who first forwards the message to the MTA).