To provide an electronic mail server system that allows even if a terminal is incapable of to possessing a plurality of mail addresses to attain transmission/reception of a mail address of an anonymous sender.

A terminal transmits electronic mail to a server 4, by using a destination resulting from partly converting a destination mail address into another address and attaching a designation address to the converted address. A mail address collation section 6, receiving the electronic mail, uses the mail address to retrieve a database 7; a processing section 8 interprets the destination of the electronic mail sent by a designated address, when the mail address matches the mail address of the database 7, converts the sender mail address into an alias mail address of the database 7; an electronic mail transmission reception control section 5 transmits the electronic mail, converts the alias mail address of the electronic mail into a mail address of the database user 7, adds the designated address to the user mail address and partly converts the resulting address; and the electronic mail transmission reception control section 5 transmits the electronic mail.