here is a major problem: what to do when a person accidentally press the unsubscribe button and then realize that they made a mistake? The system can not reverse it and people are off the charts. How to fix it?
I'm sorry some of your contacts are unsubscribing by accident. Currently, the only method to get them back on a list is sending them the sign-up form page and then they have to confirm their subscription in a follow-up confirmation e-mail.
Also, in case you want a refresher on how to re-subscribe someone look for this link when viewing your Unsubscribed contacts:
If you follow the steps presented in this FAQ you will be able to get your contacts re-subscribed!