Your email will still come back, and you'll see it in your inbox, but you won't see it in search results. And emails from more than 90 days before you signed up won't be imported.
I think the problem is that when you need to search for an email, you really need to know if you got anything or not. And for most of us, we can't wade through the 100s of emails we get a day. So this would really cut me off from my old email, which I think is a showstopper. Otherwise, it looks nice and interesting.