To provide a data transmitting and receiving system or the like in which data such as electronic mail or the like are exchanged in a network using accurate time information.

A certifying bureau 10 provides certification to a certification mail server 20M so that the server 20M issues an electronic postmark including highly precise time information. The server 20M on the transmitting side of the electronic mail puts an electronic postmark to which highly precise time information is buried to the electronic mail transmitted by a transmitter. The electronic postmark data to which time information is added by the server 20M are made unalterable by a prescribed electronic postmark issuing program, ciphered and transferred to a receiving side mail server 50M.