The coolest dummy smtp server youll ever come across :-)
Smtp4dev is a smtp server you install on your desktop.
When installed and running all you need to do is configure your application to use yout loopback ip 127.0.0.1. From now on, all mail gooing through the smtp server wont be sent, but instead, you can open them in your local mail client, and see the content you sent out. This is great for developing mail applications, both securing that you dont sent dummy/test mails to real recievers, and giving you the oppertunity to see how the mail look before it it sent.
Tjek it out at CodePlex: http://smtp4dev.codeplex.com/