Leadcamp is pretty powerful. I have not even scratched the surface but just for the read email feature, I found it immensely valuable. Within Gmail as a new email appears it shows you a whole bunch of stats. If you had emailed them prior it will show you when they read that email and how long it took them to reply. It then gives you an option to rate that reply so you can revisit the various kinds of responses. Since I am not using this for Marketing I have not scratched the things it can do but just for this, I found it useful.