javascript submit default value for unchecked checkboxes

In my form, I have a series of checkboxes for the user to agree to certain things. I don't need them to check them all or any specific ones, but I DO need the recipient of the email to easily tell which ones were not checked (terms they didn't agree with)

I have tried adding a hidden checkbox with the same name, but when the visible checkbox is checked, the email gets both responses, resulting in a confusing email.

Radio buttons aren't the answer because I just want the user to see a checkbox and check it (or not!)

fyi, php is not an available option. I would prefer javascript or jquery.

I'm not good with javascript but I tried the following and it didn't work (it sent both responses when the visible one was checked):

<input type="hidden" name="Name1" id="Hidden1" value="NOT ANSWERED" checked />
<input type="checkbox" name="Name1" id="Visible1" value="Yes" onchange="document.getElementById('Hidden1').checked = false;" />