JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Please check this guide: http://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question. This feature is to simply stop the same email address from submitting to your form. However, it's not possible to just block a single email address from a specific submitter.