From an outside perspective, it seems like your organization could very much do something about the last item. Make the unsubscribe link unique to each user. Th

From an outside perspective, it seems like your organization could very much do something about the last item. Make the unsubscribe link unique to each user. Then whether they click the link or hit reply 99.99% of the time, you have a way of uniquely identifying an individual. There's probably a lot going on under the surface though, since this seems like a pretty obvious approach.