Getting to InBox Zero is inefficient or, as Khe Hy says, a “treadmill to nowhere.” While you absolutely must respond timely to emails (i.e., within 4 hours), you also need boundaries and a system for processing them.
I check emails about 30 minutes after I wake up, then not again until after I work out and eat breakfast, and do not check them after dinner.
I process most of my emails through a Quick Step I created in Outlook. Through a shortcut key – CTRL+SHIFT+1 – emails that I have processed (read and completed) are sent to a folder called @processed. I handle most of my emails this way.
Emails that require more time for a reply (e.g., because they contain attachments I must review or ask for an opinion) I move to @to-do with another shortcut key – CTRL+SHIFT+2. Besides these two folders, I have folders for tech, marketing, management and suasponte.
At the end of the day, I usually end up with less than 100 emails in my InBox. And I’m fine with that, because I have responded timely to everything.