Review: 6 Chrome extensions let you track your Gmail

When you send an email, it can sometimes feel as if you're tossing it into a black hole. Did your recipient get it or was it waylaid by a faulty spam filter? Was it ever read or did it get lost in the day's mass of messages? The only way to tell is via email tracking, which lets you know when your email is opened by its recipient.
If you're a Gmail user, you already know that Google's service doesn't have email tracking. But if you use it through the Chrome browser, there are several services t