I switched the date order on my inbox the other day, which made me realise I have kept every since piece of “proper” email (i.e. not newsletters, and so on) since July 2006.
That means I have, right now, 34,746 emails in my Apple Mail inbox (about 17 being worthy of keeping a day), which is an amalgamation of 2 main accounts - personal, and work.
I haven’t added any to folders, nor have tagged them in any way. Occasionally I use Smart Folders to simply group emails from certain individuals depending on what my current projects are (though I only have three smart folders active right now - it’s never more than this).
When I have to get back to an email or respond to it, I flag them. This effectively becomes my to-do list, and I can see all the flagged items at once using the Flagged shortcut in mail. (The flagging functionality introduced in iOS 4.something was the single greatest advance in the iPhone in my opinion.)
As soon they have been responded or actioned, I un-flag. I usually start from the oldest and work my up. If a flagged message is really old, and nothing untoward has happened or the message is now irrelevant, I un-flag it, and will never return to it again.
At any given time I have less than 50 flagged items. If there is more than that I just have to make a concerted effort to go through them, but it’s never a case of trying to achieve “Flag Zero” - there will always be flagged items there, and accepting that means I’m never overwhelmed or stressed by it.
If I need to find something, full text search across every single email has never let me down, and it’s always super fast (in Mail, or in Gmail).
Ultimately this works if you accept you’ll never achieve inbox zero, and aren’t interested in the administrative overhead that comes into filing messages, this works well.
Finally, because of this - I don’t understand why so many people and companies are trying to fix the “email problem”, since email is only really a problem for the <1% of people who receive hideous amounts of email.
Email works fine if you just accept what it is: mainly messages between a person to person. If you use email to handle support requests, blog submissions, and so on, there are much better workflows you can use to help. Email won’t help you here.