This is the main window of Atomic Mail Verifier where you can enter a list of e-mail adresses that you may verify. In the Result tab you will be shown if the mailbox exists or not 

The Verify menu allows you to verify e-mail adresses, domains or syntax and from here you can also reset the verification status 

The Settings window lets you customize Atomic Mail Verifier's settings. Here you can see the Proxy Settings tab in which you can select the Proxy type