I came across testing a feature that ends up sending a mail. And to my misfortune i do not have access to the smtp server from my test environment. So i was looking out for a mock smtp server kind of stuff and ended up happily with test smtp server.
Devnull SMTP server is a dummy SMTP server that can be used for testing purposes. It helps you see all communication between a client and the server and is very useful if you are trying to find problems with your email server or a client that you wrote. And the best part is it is very simple to use and it is free of cost too. So if you have any such necessity do try this out.