If you want to ensure that the email submitted in your form is valid, you can let your form send out a validation email before completing the submission. This forces your user to look into their inbox and click on the link in the email in order to confirm that the email address they are using in the form submission is their own.
Of course this only works for forms that include an email field. This is a very secure way to avoid bot messages and registrations, but also decreases your form’s conversion rate, which might be a reason why very few form builders offer this function yet.
However, this is how a setup of the function would look in Caldera forms: