To register information of a receiving counterpart in advance irrespective of the accuracy of a filtering and send a mail only when the receiving counterpart authenticates, so that an information leakage by a mail erroneous sending is prevented.

A sender of an e-mail registers a user ID as a destination permitted to send a mail to a sending permitting control table. A mail control server sends an authentication mail to a recipient of the e-mail, and the recipient of the e-mail accesses an authentication page of an authentication control server to input authentication information. The authentication control server inquires the authentication information to an authentication information control table, inquires a sending permission of the authenticated user to the sending permitting control table controlling users who are permitted to send by using the user ID as a key if the authentication information is coincident, and notifies the sending permission to the mail control server. The mail control server receives the sending permission from the authentication control server and sends a text of a mail to the recipient of the e-mail.