Mail exchange between users of network game

A server group includes a mail server and multiple game servers that provide different games. The mail server includes a character information table where a character name used in each game is registered and associated with a user and a game name and a mailbox prepared for each user. When receiving a request for using an extended mail address from a terminal apparatus, the mail server generates an extended mail address including the character name as a mail account and the game name as a domain, referring to the character information table. When receiving the mail using the extended mail address as a destination address, the mail server stores the mail to a mailbox of the user corresponding to the extended mail address.