How can you limit registrations to no more than 1 per email address?

We have had someone now enter our contest registration well over 800 times which is causing us to almost be out of space in our account.  Is there a way to limit registrants to no more than 1 per email address?

Yes, you can enable the Unique Question feature to your form. It means that when the email address is already registered the form would not accept the submission again using the same email address. 

To enable the Unique Question to your form, please follow this guide: https://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question

If you want we can clear the 800 spam submission to your form. Is that okay with you?

I hope that helps. Let us know how it goes.