This is a dummy SMTP Server for testing and debugging software that sends mail.
Without configuring SMTP in the DEV environment, developers can rely on this tool to test mail sending functionality in SharePoint with this tool.
How to configure
In the Central Admin, navigate to Out going Mail settings page (http://[sharepointserver]/_admin/globalemailconfig.aspx) and provide your machine name as the SMTP server and provide a dummy email address for 'from' and 'reply to' address and save the settings
Run this tool and provide your machine name in the domain name column and ensure that the listener interface is set to 0.0.0.0 (which monitors all mails)
One of the main advantage is, it wont send mail to the actual user , so you won't end up flooding with too many mails in the inbox while testing your solution.