Whenever someone unsubscribes from receiving emails they'll have a chance to provide additional information to help you understand why they opted out of future messages. The survey they will be presented with gives 5 options which allows you to get a better idea of how your audience is responding to campaigns and what changes you can make to help prevent individuals from unsubscribing in the future.
The unsubscribe survey can be viewed per list, showing exactly how individuals responded. This helps you gauge the health and deliverability of a list.
To access:
After clicking on Unsubscribe Details, you'll be able to see a pie chart of the amount of reasons and a list of each unsubscribe in the list and the specific reason they unsubscribed.