Yesterbox seems to be an interesting approach for handling large amounts of email.
Instead of going though today’s email which fills up throughout the day and largely ignore the incoming stream of mayhem, focus on handling email from yesterday instead. That way, there is always a finished state, since no new email message can fill up the queue from yesterday.
There are of course times when you really need to reply to an email today, and the model supports this scenario as well. Just get going on the old email and as a “reward”, you may answer important email from today as well.