If I recall correctly it was obvious in Acy 5, but I just can't find it in Acy 7.
If you enable the unsubscriibe page in your configuration a field is shown where users can add their reason for unsubscribing.
Ok, and where can I find the reasons, my unsubscribers wrote in the field?
Thanks in advance,
That information is stored at user level in the user history.