Having been there, repeatedly:

First, be ruthless and just delete any unanswered email you don't have to respond to or otherwise react to. It's unfortunate and makes some people unhappy, but if you're in a hole, you need to do what you  can to get out. You can always send everyone an email explaining you're under a mountain of email and ask them to mail about the topic again in a month if it's still relevant.

Second, after you've dug yourself out from under the mountain, maintain the ruthlessness until you feel you can stay on top of things easily.

Third, if you haven't already, consider introducing a system for managing email (and other inputs) and actions that should result from that. I happen to favour Getting Things Done (http://gtdfh.branchable.com/) but whatever you fancy and works for you is fine.