The Internet’s current architecture de-couples the cost of sending traffic from the consequences of sending traffic. Its open nature allows anyone to initiate a connection with minimal authentication. These factors account for the excessive consumption caused by spam in the email system and other service areas. At the network layer, resource consumption caused by spam is analogous to Distributed Denial-of-Service (DDoS) attacks. We believe the two taxonomies proposed in this paper (of spam definition and of spam sending mechanisms) are the first comprehensive study of spam over different service areas. Our taxonomies will help in comprehending the similarities and differences between traditional Email spam and related newer problems such as SPIT (spam over internet telephony), SPIM (spam over instant messenger) and Web spam (spam over search engines, which misleads search engines into ranking some pages higher than they deserve).