COAT : Collaborative Outgoing Anti-Spam Technique Adnan Ahmad and Brian Whitworth Institute of Information and Mathematical Sciences Massey University, Auckland, New Zealand [Aahmad, B.Whitworth]@massey.ac.nz Abstract. Spam and anti-spam techniques are part of email since its birth. Spam is electronic garbage with no anticipating recipient and almost always deleted. In 2010, around 89% of all emails were spam, resulting in an estimated 260 billion spam emails sent every single day. Most of the current anti-spamming systems focus on incoming spam but these messages still travel the internet world and waste bandwidth, storage and processing resources. This research proposes a collaborative outgoing anti-spam technique to reduce the spread of spam on the internet. The technique targets outgoing emails and its use would free the internet from 260 billion spam a day. During real-time experiment, it blocked 99.95% of the total spam generated with 99.57% elimination at sender side. Keywords: Anti-Spamming, collaborative, outgoing. 1 Introduction Simple mail transfer protocol SMTP [1] is the common mechanism for transporting electronic mail among different hosts reliably and efficiently. Most email systems use SMTP to send messages from one server to another, which then retrieved by an email client. SMTP is a relatively simple, text-based protocol, which specified some recipi- ents and then transfers the text to them. SMTP provides no mechanism for accountabil- ity and fairness and let sender place messages directly into receiver’s inbox. This si m- plicity of SMTP is exploited by spammers, who take it as a tool for marketing. Spam is electronic garbage that wastes internet bandwidth, storage, and processing [2]. Over the past years, opportunistic sending of static messages through compromised hosts has evolved into dynamically generated, subtly obfuscated messages sent on a massive scale by special purpose malware. Unsolicited email creates problems for internet, clogs mailboxes, slows the servers and lowers the productivity. Although current spam prevention techniques have achieved some success in reducing the amount of inbox spam, the spam sent is still growing from 87.7% in 2009 to 89.1% in 2010 [3]. The arms race between spamming and anti-spamming techniques is ongoing. As filters improve and block some types of spam, spammers develop permutations to defeat the filtering technique. Besides, increasing efficiency at receiver side does not stop an increase in inbox spam sent, resulting in the same (or even more) spam mes- sages in the end users’ inbox. Also, current anti-spamming techniques work to prevent malicious mails ending up in the inbox. But it is not sufficient to save inboxes, when spam affects the whole internet. To address this issue, needs more sophisticated tech- niques to prevent the spam affecting not only the inbox but the whole internet as well. The rest of the paper is organized as follows: Section II summarizes the current state of the art. Section III describes the method adopted for COAT implementation details. Section IV explains the results, while section V concludes the proposed work.