Behavioral characteristics of spammers and their network reachability properties

By analyzing a two-month trace of more than 25 million emails received at a large US university campus network, of which more than 18 million are spam messages, we characterize the spammer behavior at both the mail server and the network levels. We also correlate the arrivals of spam with the BGP route updates to study the network reachability properties of spammers. Among others, our significant findings are: (a) the majority of spammers (93% of spam only mail servers and 58% of spam only networks) send only a small number of spam messages (no more than 10); (b) the vast majority of both spam messages (91.7%) and spam only mail servers (91%) are from mixed networks that send both spam and non-spam messages; (c) the majority of both spam messages (68%) and spam mail servers (74%) are from a few regions of the IP address space (top 20 "/8" address spaces); (d) a large portion of spammers (81% of spam only mail servers and 27% of spam only networks) send spam only within a short period of time (no longer than one day out of the two months); and (e) network prefixes for a non-negligible portion of spam only networks (6%) are only visible for a short period of time (within 7 days), coinciding with the spam arrivals from these networks. We discuss the implications of the findings for the current anti-spam efforts, and more importantly, for the design of future email delivery architectures.