After posting it on Reddit, I've got advice to change it into something that would help people constantly, rather than once in a while. Mass unsubscription is still planned, but I've realized there is much more that can be improved: visual distinction of important emails, quick previews, automatic email confirmations, keyboard actions, and probably a lot of other things.
Here is a quick poll, which feature would you prefer? https://app.handypolls.com/p/XALk0K