I've never understood why busy people don't use staff to "pre-clean" the inbox. Especially if you get dozens of emails a day. After a vacation (heck, every day), I spend a lot of time deleting spam, daily reports, and threads I'm cc'd in (but get resolved by others).
For 3 years now, I've had a full-time assistant who filters all my email, handles the FAQs, and only leaves a few per-day for me - just the ones that only I know the answer to.
Anyone interested in this, feel free to email me for details.
Most of my friends who have admin assistants do have their admin assistants do this. The admin assistant prioritizes every incoming email.
They respond to the ones they can, forward on emails better suited for other people and flag important emails for their boss