Analysis of spam mail sent to Japanese mail addresses in the long term

Today e-mail is a indispensable communication tool because of wide spread of Internet technology and many spam mails are delivered in the Internet. In order to avoid spam mails, spam filter is used in many mail servers or PC. It checks the content, sending address or so on of a mail and decides whether the mail is a spam mail. After spam filter works well to remove spam mails, spam senders improve the methods of sending spam. Spam filter technology and spam sending method make a vicious circle. Ending this vicious circle needs spam mail characteristics including the change according to spam filter improvement. This paper analyzes spam mails which are saved in the long term in order to obtain spam mail characteristics and reports the result of this analysis.