To provide a means for efficiently transmitting/receiving electronic mail in large size.

Inside an electronic mail server device, a flag is provided in one-to-one correspondence to electronic mail account, this device is provided with a means capable of arbitrarily setting the setting value of the flag from an electronic mail client device and corresponding to the setting value, only the prescribed number of characters from the head of mail data addressed to the electronic mail client device are transmitted or only the text except an attached file is transmitted.