| 摘要 |
PROBLEM TO BE SOLVED: To provide an electronic mail system that secures the security of transmission of electronic mail by a certificate and a signature and changes the security of decision of the certificate so as to select ease of use or a degree of the security depending on the policy. SOLUTION: An electronic mail server 5 receives electronic mail from terminals 2, 3, 4, a relay server 6 receives electronic mail from the electronic mail server, transmission of the electronic mail to an external domain is inhibited as the fundamental settings and the transmission of the electronic mail to the external domain is permitted when a specific condition is established. Furthermore, the terminal generates a file certificate to certify contents of an attached file in the case of generating the attached file, signs the file certificate to warrant the relation between the attached file and the file certificate and the contents of the attached file, and the relay server decides the propriety of transmission of the electronic mail to the external domain on the basis of the file certificate and the contents of the signature attached to the attached file sent from the terminal and transmits only the electronic mail with the permitted contents to the external domain.
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