Power users already know about the magic of the proxy icon—the tiny icon that appears in the title bar of most windows. But Hints reader arti.66 found a unique benefit to the proxy icon in Apple Mail.
When you open an individual message in its own Mail window, you can drag that message’s proxy icon to any desktop window to create an Internet Location File (.inetloc) that points right back to the message. If you want quick repeat access to an important e-mail, using the proxy icon essentially allows you to create a desktop bookmark.
Of course, you can place this pointer file anywhere icons can go; that means you can drag the proxy into your Dock, or even drag it onto a new blank message—which adds the original message as an attachment.
Note that you can use the favicon in Safari—that’s the icon in the location bar immediately to the left of the URL—in the same way.