There is provided a method of issuing a mail address to a user who makes e-mail communication with a mail-receiver through a server, including (a) on receipt of a request from the user to issue an interim mail address, issuing an interim mail address to the user from the server, (b) determining a threshold based on which the interim mail address is judged whether valid or invalid, (c) judging whether the interim mail address is valid or invalid, based on the threshold, and (d) if the interim mail address is judged valid, allowing the user to make e-mail communication with the mail-receiver through the use of the interim mail address in place of a mail address of the user.