In Internet, today most widely issues occur with security. Security plays the vital role in Internet. Many software and hardware systems are affecting with the security issues. This may cause major problem for the companies to maintain the network securely. Attackers mainly concentrate on attacking the servers and systems with any type of malware and virus to hack the system or mail account. Today the most popular attacking by the attackers are spam mails. This brings lot of security issues if it is implemented in gmail, yahoo and other mail service providers. Spam zombies are the spam activities done by the spam developers to attack the system. In this paper, an ensemble spam mail detection system named ESMDS by observing outgoing and incoming messages of a network. ESMDS is developed based on a powerful analysis tool called Sequential Probability Ratio Test (SPRT). Results show the performance of the ESMDS.