I am uncertain about the name but the folks at http://www.yesware.com/ have created something useful for financial planners (and others). It replaces "read receipts" and is a plugin for Google Apps or Gmail. It puts a small pixel in any emails you want "tracked" (you can toggle tracking on and off) and you get a status bar at the top saying whether the email has been opened, time/date and on what device. Useful information.
You might have noticed that I have tagged this post "compliance". Well it does allow for confirmation that an email has been opened. This is not the same as confirming it is read I grant you but certainly better than normal post where you are left in the dark about receipt.
It is certainly interesting to note the time taken for an email to be opened and a response. You can learn something about how urgently your clients treat your emails or whether your prose is in fact unfathomable!