The 'From' field should be an email that belongs to the domain where the form is running. In the 'Take the code wizard', 'Email settings' page update the 'From' field to an email that belongs to the same domain.
For example, if your website is www.abc.com, the 'From' field should be of the form firstname.lastname@example.org
Most Email servers validate incoming emails. The SPF validation checks the 'From' field of the email to prevent source address spoofing (See the details here)
Make sure that the 'From' field belongs to the same domain as the website where you are running this form.