This feature has no native way of becoming re subscribed. When a person does unsubscribe to all it does not turn on DND on emails. For people who unsubscribe you can no longer email them even with relevant important information about their order such as delivery etc. This feature is at the moment very dangerous in terms of being able to still communicate with customers, they think they are unsubscribing from marketing yet are making it so they can no longer be contacted.....