Is there a way to ensure a field's uniqueness through Jotform?

For instance, when a user submits their email, a webhook triggers and enters their data through our API. We need to be sure all emails submitted are unique. Can our webhook endpoint respond with a message that will then be displayed to the user? Alternatively, is there a way to ensure a field's uniqueness through Jotform?

The option to ensure a unique email can be setup in JotForm, please check this guide: https://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question

Let us know if you need more help.