What's the point? How many people actually keep fewer than 10k unread messages in their inbox?
I think you either have 0 or 10K+.
Most people.
If you have 10k+ unread messages, it's time to introduce some filters to mark them as read.
It turns out I only get around 5 personal e-mails a day out of the 100+ I actually get. Which could be read either way :).
Unless of course I go on vacation and then I have an hour or two to get back to NORMAL.