1. Unsubscribe from useless or even useful information you don't have time to read
2. Prioritize email first. That's probably your primary way to communicate professionally, be tidy and respond quickly.
3. I noticed that I needed to cut down on vising RSS readers, instead I had what I want to follow sent to my inbox.
4. I wrote a series of apps trying to turn my inbox into my news feed (but better), it made it easier to me to go through. Similar, to the people (all of us here) probably visit HN or Reddit to cruise through and get informed, and interact. Originally, I wrote something to send me jokes[2], then interesting stories & investment information [3]
5. I laid out my inbox so I can quickly prioritize. For instance my gmail had different domains organized on the right (3 - 4) and the center was all email. This let me target the more important emails. Now, I have something similar on fastmail.com
6. Just to emphasize you have to check emails every morning and night and just constantly try to keep your count at zero. I actually leave my inbox full of hundreds of email, but spend about an hour cleaning up a month (back down to 20 or so - keeping the necessary threads).
7. Use your desktop. It's easy to use mobile for most things, but your desktop is a real work horse when it comes to quick replies, categorization, and deletion.
Each mailbox can typically be gone through rapidly in a batch a couple times per day to get your unreads to zero.
If something requires followup or reply, record that fact in an external system rather than using the inbox as a to do list.
Oh, and get your colleagues to move away from email as a default medium for conversations.
That with keyboard shortcuts to mark all as read and archive does the trick for me.
2017
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Email is not a task list.