Prevent Duplicate Entries

How do I prevent duplicate entries on my forms?  In other words, if an email was already used previously, and that email is being used again, I want the person to get a message that tells them that email already exist.

Hello,

You can enable unique questions on your form and set the email address field as your unique field. This way, it will only allow the email address to be submitted once. Further submissions of the same email address shall no longer be allowed. You can refer to this guide on how to enable the unique question feature on your form: https://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question

If you have questions, please let us know.

Thanks.