This story needs context. Unless we know why the user quit using DynDNS, there's no real way to determine whether an appeal like this effective or even appropriate.
For example, I used to use DynDNS all the time because I was running a small personal site off my home broadband connection. Then, thanks to an improvement in fortunes, I was able to afford a hosting service and a "real" DNS. So I switched. If DynDNS sent me an e-mail like this, it wouldn't really matter, because I've already got everything set up, and I'm not really looking to change.
For example, I used to use DynDNS all the time because I was running a small personal site off my home broadband connection. Then, thanks to an improvement in fortunes, I was able to afford a hosting service and a "real" DNS. So I switched. If DynDNS sent me an e-mail like this, it wouldn't really matter, because I've already got everything set up, and I'm not really looking to change.