1. Field of the Invention
The present invention relates to an electronic mail distributing apparatus and an electronic mail distributing method which distribute e-mails to registered e-mail addresses, a program for controlling the method, and a storage medium storing the program.
2. Description of the Related Art
To provide and share information on the Internet, electronic mails or e-mails are widely used not only on a one-to-one basis but on a one-to-many basis and a many-to-many basis. For example, company's advertising mails are distributed on a one-to-many basis, and mailing lists are used on a many-to-many basis. In either case, an electronic mail distributing apparatus is used to distribute e-mails to many people.
The electronic mail distributing apparatus is capable of receiving e-mail addresses from persons who wish to have e-mails distributed and registering the received e-mail addresses as destinations of e-mails to be distributed, deleting e-mail addresses registered as destinations of e-mails to be distributed, and receiving information from an information provider and distributing e-mails containing the received information to registered e-mail addresses.
The electronic mail distributing apparatus can be used by unspecified persons. In the case where an e-mail subscription is made on a Web, the user can subscribe to e-mails only by causing a user terminal to display a HTML page prepared in advance for e-mail address registration, enter an e-mail address in the displayed HTML page, and send the same to the electronic mail distributing apparatus. In the case where an e-mail subscription is made by sending an e-mail to the electronic mail distributing apparatus, the user sends an e-mail with a word “subscribe” in the body thereof to the electronic mail distributing apparatus so that his/her e-mail address can be registered as a destination of e-mails to be distributed.
However, such a simple system of making an e-mail subscription raises a problem in terms of the security because an unauthorized third party other than a person who owns an e-mail address can make an e-mail subscription. If an unauthorized third party other than a person who owns an e-mail address makes an e-mail subscription, e-mails are distributed to him/her, and hence he/she receives undesired e-mails. Namely, the electronic mail distributing apparatus can be used to attack user terminals of many unspecified persons.
To counter such attacks, an electronic mail distributing apparatus has been proposed which sends a subscription confirmation e-mail to a user terminal in response to an e-mail subscription having been made. The subscription confirmation e-mail is sent to an e-mail address which has been registered. If the recipient has no memory of having subscribed, he/she can unsubscribe using the subscription confirmation e-mail. Also, an electronic mail distributing apparatus has been proposed which does not send subscription confirmation e-mails, but distributes e-mails including instructions on how to unsubscribe.
Further, a variety of techniques have been proposed to counter attacks using e-mails (for example, Japanese Laid-Open Patent Publication (Kokai) No. H11-167533, Japanese Laid-Open Patent Publication (Kokai) No. 2000-10800, and Japanese Laid-Open Patent Publication (Kokai) No. 2002-64531). Specifically, an electronic mail firewall is installed on a recipient's terminal according to Japanese Laid-Open Patent Publication (Kokai) No. H11-167533, a device which rejects reception of predetermined mails is installed between a mail server and an electronic mail distributing apparatus according to Japanese Laid-Open Patent Publication (Kokai) No. 2000-10800, or a mail server is provided with a mail rejecting function according to Japanese Laid-Open Patent Publication (Kokai) No. 2002-64531, so that predetermined e-mails can be rejected according to description patterns thereof. Namely, e-mails to be rejected are selected by referring to titles thereof and sender's e-mail addresses.
However, according to the method in which a subscription confirmation e-mail is sent and the method in which a description of instructions on how to unsubscribe is added to e-mails to be distributed, the user cannot counter attacks until he/she receives the first e-mail (i.e. a subscription confirmation e-mail or an e-mail which is distributed for the first time). Further, after unsubscribing, the status before subscribing is restored, allowing attacks by repeated subscription by an unauthorized third party. Namely, subscription confirmation e-mails themselves can be used for attacks.
Further, although in Japanese Laid-Open Patent Publication (Kokai) No. H11-167533, Japanese Laid-Open Patent Publication (Kokai) No. 2000-10800, and Japanese Laid-Open Patent Publication (Kokai) No. 2002-64531 that counter e-mail attacks, repeated attacks using e-mails as above can be prevented, it is difficult to find out and register description patterns of e-mails to be rejected. The titles of e-mails and the descriptions of sender's e-mail addresses do not necessarily include information which specifies an electronic mail distributing apparatus. A plurality of mail servers may be managed on the basis of the same sender's e-mail address, and e-mails to be distributed are not necessarily titled in specific patterns which are uniquely determined for each mail server. Therefore, determining whether e-mails are to be rejected or not according to their description patterns may cause necessary e-mails to be rejected or cause unnecessary e-mails to be not rejected.