how to send 'no' in form when checkbox isn't checked in wp

In contact form 7 plugin of wordpress, is it possible to send custom message to mail based on checkbox value. In my form I have, subscribe to newsletter checkbox. When user checks the checkbox, subscribe to newsletter is coming as 'Yes' in mail.Now I want to send subscribe to newsletter as 'No' when user doesn't check the checkbox.

Is it possible. I tried and am still searching for the answer in google but to no avail.Any help/suggestion is welcome. Thanks in advance.