Trash, Archive, Folders in Folders, Tags, forget it!
Where is it? In the Inbox. If it's unread, I need to do something, if it's read, I don't.
Although if my clients start to slow down, I will export and delete the oldest year from my personal email. So I guess I do technically archive. But only in bulk and begrudgingly.
In Gmail you can set it to group all unread at the top.
Sometimes I'll open an email and mark unread again if I need to come back to it.
My inbox was at about 100k _unread_ emails with about 280k total.
I am happy to say I am now at inbox-zero (ish).
What if you read an email, and need to do something, but can't do it right now? Do you mark it as unread so you can deal with it later?
I did that for years. Thankfully no longer!
Rinse, repeat
Now I have a keystroke that will automatically create a TODO with a link to the message. I hit the keystroke and then archive so it no longer shows up in my inbox.
There are lots of poor productivity books/hacks, but the "Do not treat your inbox as a TODO list" has stood the test of time.
It's self-culling with time. I've got unread messages deep down on the list. Things that I wanted to do something about months ago, but never did, and they weren't important enough to come up again. And if they ever do come up again, I can see that I received a message and didn't do anything with it.