I've adopted the inbox zero approach. If it's important it gets reclassified onto my task list with start and end dates, if it's useful info it gets filed, and everything else goes into trash.

At this point I am thinking my Thunderbird should probably just unify the Inbox view and the Task view, since it would be a more accurate representation of how I view email.

I thought just now, isn't inbox zero just a cosmetic difference?

For you: important things become tasks, useful things are filed, and everything else gets trashed.

For me: important things get opened and replied to. Useful things are starred (and opened). Everything else stays untouched.

And that pesky unread number is irrelevant because I mute all notifications. I'm not discounting your method, I am just now realizing the circle of it all.

There's a UX difference: when you look at your inbox from fresh you have to remember which ones you purposefully ignored because they were left unread in the inbox (this might be trivial for you if you're used to it).

I practice inbox zero also, the value for me is knowing that if it's in my inbox it's because it requires actioning, if it's not it's ignored (deleted or archived).

I also just generally like deleting things as much as possible, I don't like the cruft. If I have to search through old emails I don't have to filter by stars or anything like that, I like knowing that if it exists it's because it's important.