Search with "AND" and by single recipient
Search would be greatly improved if you could search with "AND" instead of "OR." If fifty emails contain the word "camping" and only one contains "Michigan," there's no easy way to pare down the list of 50 emails to quickly find the one.
The next huge improvement to search would be to search for emails from only one sender to only yourself, as opposed to each of you as recipients of a group email. If you and John are part of a group exchanging scheduling and policy emails 50 times a day, but a month ago John sent you a personal email inviting you to dinner and you can't remember what date he suggested, you have to scroll through hundreds of unrelated emails to find that one.