There’s a useful productivity addition in Mail that’s easy to overlook. At the top right of the message list is a circle with three lines in it; click that to turn on filtering for the mailbox or search results you’re viewing. Initially, the messages below are filtered to show only unread ones. To the left, click the filter’s description to set its criteria, such as whether a message is flagged, sent directly or copied to you, has an attachment, or is from someone you’ve set as a VIP contact. Click the icon again to turn off the filter; the app remembers your criteria choices for individual mailboxes.