This is the niftiest little piece of software I have ever found! Once installed and set up you never know it's even present but it is always working for you. I send out a lot of important emails, often to people who don't even know me yet and Readnotify tells me if and when that email was opened, how many times, duration, if it was forwarded on etc.When I talk with my clients later there is no guessing whether they have received my communication. I already know the answer!
Totally unobtrusive, invisible and completely reliable. Even more, it is very inexpensive and there are never any ads or promos. In six years of use I have contacted customer service twice for questions around some advanced settings and they replied within a day with an acceptable response. I have it installed on every pc in house and on my subs pcs as well.