How do i attach a value for if a checkbox is checked in HTML?

I want to make an assignment where people look up an e-mail on a list of websites. If there i no e-mail to be found, i want them to check a box. If they check the box i want it to return a value like: "no e-mail found". Is there an easy way to do this? im holding a survey in Amazon Mturk.

Below you can find my current code. I have barely any knowledge on HTML.

https://i.stack.imgur.com/iVQBP.png