To provide an electronic mail system capable of respectively setting destinations requesting sealing confirmation at the time of transmitting of a mail, editing a message format of the return mail, or replying the mail at the time of reception or after the sealing.

This electronic mail system comprises electronic mail server devices 30, 40 connected to a distributed network 20, a mail box device 60 connected to the mail server devices, and terminal devices 100, 120 connected to the electronic server devices. The terminal device comprises a function means capable of transmitting a return mail to be transmitted in response to a request for confirming of unsealing at the time of reception or preparing a return mail even after unsealing, and a function means capable of specifying solely specific destinations at requesting of confirming of unsealing.