| 摘要 |
PROBLEM TO BE SOLVED: To provide an electronic mail system that allows a mail client to flexibly cope with encryption of electronic mail and its transmission based on the acquisition result of a public key from a mail server or the notice of verification result of the validity of the public key. SOLUTION: When reception sections 12, 13 of the mail server 10 receives electronic mail, destination information and an encryption instruction from the mail client 30, a public key acquisition section 14 acquires public keys of destinations included in the destination information, a verification section 17 verifies the validity of the public keys and an encryption section 20 encrypts the electronic mail by using the public keys for the destinations. When there exists a destination whose public key cannot be acquired or a destination whose public key is discriminated invalid, the mail server 10 informs the mail client 30 about it. The mail client 30 receiving this notice recognizes destinations to which transmission of encrypted documents is disabled so as to selectively execute stopping of the encryption transmission of electronic mail or encryption transmission or the like only to destinations to which encrypted documents can be delivered.
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