Full Subscribe/Unsubcribe reporting
One of the things I do is track my opt-in rates for various ARs. It would also be good to track opt-out (unsubscribe) rates for those ARs as well.
If I got a bunch of unsubscribes, I could see what emails I sent that may have driven people away (e.g. too many promotions)
It would be ideal to do this for a given time period - say 1 month, 1 week, 1 year, etc.