Sidekick Lets You Know Exactly When Someone Reads Your Gmail Message
I have just started using Sidekick by Hubspot. It is a Google Chrome add-in that lets me know when someone has opened an e-mail I sent. Sidekick is a much better solution than sending a Read Receipt. You are limited to 200 notifications per month, but that's not bad - because you can check the little check box in the bottom right corner and then click the orange (instead of the normal blue) Send button when you want to use it. I don't really need to know exactly when each of my email recipients opens my message, but for some of them, I really do want to know. When you check the Sidekick checkbox and send the message, it is tracked, and as soon as your recipient opens it, you receive a popup message in the lower right corner of your window.
Another feature that I really like is the Sidekick link at the left of my Gmail (known as a Label) which I can click on and see all of the emails that have been tracked. It shows each person's name and picture (if they have one) and the views of each message. You will see when and who opened the message, which is also great for when you send something to multiple users. I can definitely understand why someone would pay for this product. Businesses will get the ability to track Clicks and a Salesforce section, each with their own tabs along the top in what is called the Activity Stream.
I'm just starting to use this product in its semi-limited free version, and I like what I see so far. If you use Sidekick or are thinking about trying it, I don't think you will be disappointed at all.