Also, if you view a contact in the contact list, it will show you some of the most recent correspondence with that person. And if you hit the menu button there's an "Activity Log" option that shows you everything from that contact. Emails, phone calls, probably texts as well (I'm not a texter).
It's a little convoluted, but it will get you what you want. Or you could just use the new universal search. Start typing in the name of the person you're looking for, and you'll see an email icon pop up. Select that, and you'll have all the emails from that person.
BTW, this is all OS6 specific AFAIK.