I am not a inbox zero proponent. I think if you manage to get to the bottom of your email everyday, you may be spending too much time on email. I usually have about 40 in my inbox at any time. I get to the important ones then once a week I do some catch up.
But, sometimes on really busy weeks, when I’ve been on vacation, or I’ve been really lazy with email I may have more than a couple weeks of email to go through. I find the quickest way to clear out all the emails is to take a week. On Monday I will clear out all the emails from Sunday, then the Sunday before, then the Sunday before, etc. I like to go by week’s because otherwise I am afraid things from earlier week’s will take too long to get to. And it’s fun to find out that most of those older emails can be deleted or archived.
Then Tuesday I will take care of Monday’s and the Monday before and the Monday before.
In one week, the email backlog is gone.