A lot of folks aren’t aware that within Mail on iOS 7, you can search for certain message attributes in addition to finding things by a person’s name. To check this out, drag down from within any mailbox to reveal the search field if you're on the iPhone; on the iPad, Mail's search box is always visible.
It's good to know, too, that whenever you type something in the box, you can drag down again to show the toggle for either searching all mailboxes or just whichever one you’re in.
Now here’s where the searching by attributes comes in. There are certain special types of messages you can look for—ones that are flagged, ones that have attachments, those that come from people you’ve marked as VIPs, and ones that are unread. You’ll do that by just typing the appropriate word into the search box, like so:
Pretty neat, right? Keep in mind that you can always turn on the unified mailboxes for showing messages that match those same attributes, as I described in this tip. Being able to search for those things is very handy, but using the special mailboxes is the way to go if you've gotta do it all the time.