Marco Arment, in his interview with Brett Kelly:
The only way to deal with large amounts of email is to devise standards for deciding quickly whether to respond to something. And not whether you think you should respond, but whether you think that you realistically will. You have to be honest with yourself and brutal to the senders who don’t make the cut.
This is how most people work anyway, but they’re in denial about it, so they’ll let their inboxes collect thousands of messages and then “declare bankruptcy” after a while and start the cycle again.