HowtoMatrix

The Postal project includes three programs aimed at benchmarking mail server performance. The main program, postal, sends email messages to a specified list of destination addresses at a specified rate. Postal can let you see how fast your system can process incoming email and thus can help you measure improvements to your mail server when you are making software and hardware changes. For example, you can use postal to tell you whether switching to a different IMAP server will allow you to deliver more messages per second on the same hardware.

Read more at Linux.com