| 摘要 |
PROBLEM TO BE SOLVED: To provide a system and a method, with which the security of electronic mail on the Internet can be kept without depending on whether or not a security function is packaged on the side of a client. SOLUTION: A proxy 4 is located between a mail server 2 on a LAN 1 and the Internet 5, a mail server 2, which receives plane sentence mail from a mail client 3, sends mail addressed to anywhere except for LM to the proxy 4 while keeping plane sentences as they are, and the proxy 4 enciphers the plane sentence and sends signed enciphered mail to the Internet 5 after adding the signature of a mail transmitter. Then, it is checked from the Internet whether the signed enciphered mail is revised or not and when the mail is not revised, the enciphered mail is deciphered and delivered to the mail server 2 as plane sentence mail but when the mail is revised, receiving of the mail is refused so that the revised mail can be prevented from entering the LAN 1. |
