Enhance unsubscribe form to reduce likelihood of accidental unsubscribes

If recipients forward a bulk mailing to someone else who then hits the unsubscribe link - the original recipient will be "unintentionally" unsubscribed. We can reduce the likelihood of this by including a 'masked' display of the email being unsubscribe and requiring that the user enter the complete email address before submitting the unsubscribe request.

An example from another bulk mailing tool is attached.