There is a "Unique" checkbox setting for each form field. This allows you to restrict submissions of the same value in that field. For example, you can allow only one submission for a particular email address or physical address. This is great for contests, surveys, and other types of forms where you want to limit multiple submissions from the same person. You can also remove options from checkbox, dropdown, or radio button fields when someone chooses them to control inventory.
Be careful how you use this field, as you don't want to accidentally prevent people from submitting to your form by making a field unique where multiple people might need to give the same answer, such as a "yes/no" field.
If you try to submit the same info twice to a unique field, you will see an error message like the one below.
Note - It is not possible to use the unique option if you have encryption on with your form.