E-mail transmitted from a sender terminal together with an attached image file is received by a mail server. The latter inserts a tag in the header of the image file that has been attached to the e-mail. The tag includes the name and telephone number, etc., of the sender, which have been stored in a database that archives personal information. The image file in which the sender name, etc., has been inserted is attached to the e-mail in place of the image file that was attached to the received e-mail, and this e-mail is then transmitted to the terminal of a receiving party.