Get Notify

This tool maybe doesn't have the best UI but the idea of enabling mail tracking just by adding a domain to the sent email is really great because you don't need to install any add-on and every email client will work perfectly. After sign-up, you just have to add .getnotify.com to your sent email and you can get notified by email when the receiver opens the email and clicks in any links and even you can check history and more detailed information in the website.