On the SPAM blocking using the SMTP throttling

Abstract

We proposed a new method to block SPAM mail by selecting throttling and droping smtp connections using some blacklist and the argument of HELO command sent by a remote server. We implemented the method to the mail gateway server of Niigata university. In this paper, we describe how our method blocks SPAM mail and the blocking, false-positive/negative rate observed at our server. In the present method, server adminstrator does not need to manage the whitelist of mail servers. Instead of the whitelist, we use some of the well-maintaind public lists. Furthermore, we can reduce the number of the concurrent connections by selecting throttling connections using the argment of HELO command and some blacklist. After implementing our method to the mail gateway server, we do not recieved any false-positive report from our user. The arrived mails to our server and arrived SPAM mails to the paticular mail address are reduced by approximately 30% and 90 %, respectively.