An e-mail sending-receiving system that enables to ensure security at the time of sending and receiving an e-mail including an attached file encrypted and to improve convenience. In an e-mail sending terminal, a first storing unit stores a password in a storage medium in association with a receiving-side mail address, an encryption unit encrypts a file attached to an e-mail so as to be decodable using the password, a generation unit generates the e-mail by attaching the file encrypted, and a sending unit sends the e-mail to the receiving-side mail address. In an e-mail receiving-side terminal, a second storing unit stores the password in the storage medium in association with a sending-side mail address, a reception unit receives the e-mail, and a decoding unit decodes the encrypted file using the password stored in association with the sending-side mail address of the e-mail received.