Being able to filter the duplicate value of a certain field while form submission restricts users to use the same info or value more than once by others. So enabling No Duplicates option for weForms of the Advanced Options lets you do just that.
In order to activate the No Duplicates option at first, navigate through WP-admin→weForms→All Forms→Add Forms→Blank Form or choose from a Template then follow the below steps.
So now when the No Duplicates option is enabled, this is the message that is displayed when someone inputs a non-unique entry in the email address field of the form.
So until you enter a unique value in the email address field changing this duplicate value, you will not be able to submit the form.
For any further queries, contact our support team