Once you've created the new Form Submissions list, you'll notice a checkbox called Always Append. By default, this feature is disabled. By keeping it disabled, the Act-On form will allow duplicate submissions based on the email address; however, Act-On will simply update the previous form submission with the new form submission. For example, if firstname.lastname@example.org submitted the form twice, the form submission list will overwrite the first submission with the information from the second submission.
Enable the Always Append feature to allow duplicate submissions based on email addresses. For example, if email@example.com submitted the form twice, the form submission list will contain two entries for firstname.lastname@example.org and treat them as unique submissions.
Form Submission List
Once the form is created and saved, the newly-created form submission list will be located under Contacts > Other Lists > Form Submissions. If you have folders created previously, the list will be located in the Default folder. You can hover over the list, click Move to move it to a different folder within the page.