We have unsubscribe forms that contain just an email address field. If someone inputs an email address that is not already on our database, Marketo will create a new lead on the database. We would like to stop this and validate the email address at the time that the unsubscribe form is submitted. Therefore, if the email address is not found on the database, it will display a message to the user and not submit the form until they enter an email that is on our database.
Is there an easy way to do this?