I get around 50 emails a day, and hover around inbox 40 Removing all filters and categorization has helped me reach this number, and forced a few habits and mindset changes: 1: I aggressively unsubscribe from mailing lists. If you have to make a filter to automatically archive a mailing list because you never read it but want to keep it just unsubscribe. If you have to, bookmark the site but if you aren't reading it…
Two questions decide the fate of every email "Is this from a person I know?" and "Will I ever need to search for this?" If both are no, then it's destroyed with reckless abandon. All others are archived immediately. No "read" messages in my inbox, ever. It's either "unread" or it's archived.
I almost always Send + Archive, unless what I sent was "I'll take a look in a couple minutes". And then I Send + Archive as soon as I send the next reply. If it sits in my inbox for over a couple days, I add it to Asana (if I haven't already) and archive the message.
I unsubscribe to almost everything automated (besides my own daily system summaries, which I delete once I've reviewed them).
One thing I would _love_ to have is the ability to set expiration filters on my emails. For instance, I like getting travel deals in my inbox, but I never need them for more than a day (since they generally only last that long anyways). Same for system summaries: Auto-Delete or Auto-Archive after 3 days would be perfect.
Also, since I don't use a local client for email, the "Checker Plus for Gmail" Chrome extension is pretty great, since it shows everything as a unified inbox, and shows me a single "unread" number so I know when I need to dive in and do some triage.