Many custom applications require an email component, either for workflow, notification or error logging. During the development and testing phase, programmers need to be able to test whether or not the application will actually send the email. Instead of installing an actual SMTP server on Windows 7*, you can configure IIS 7 SMTP Email.
*Note: Windows 7 no longer supports the Microsoft SMTP service, so if you still want to install an SMTP server on Windows 7 you would have to install a third-party application.