Use Microsoft Exchange Server Stress and Performance (ESP), a highly scalable stress and performance tool for Exchange, to simulate large numbers of client sessions by concurrently accessing one or more protocol servers. ESP includes multiple modules that you can use to simulate a wide variety of protocols and loads. You can run modules concurrently from multiple hosts, thereby more realistically simulating physically separate client machines. There is no limit to the number of computers on your network that can host ESP modules.
Note: The ESP tool does not have the capability of creating users. Therefore, if you want to create a test that involves simulating actual individual users, and not simply client sessions, it is recommended that you use ESP in conjunction with other tools that create users (for example, Exchange Load Generator).