In a mobile communication network system provided with a cellular telephone enabling use of mail service for mobile terminals using a mobile communication network and Web mail service, and a server apparatus that manages e-mail addresses assigned to the cellular telephone for both the mail service, already input information is stored in the terminal when creation of Web mail is suspended in the cellular telephone, while the stored information is transmitted as an e-mail in the mail service for mobile terminals, and when the server apparatus receives the e-mail, the server apparatus replaces an e-mail address of a sender with an e-mail address for the Web mail service to transfer.