So you not only help me with newsletters but also help to find the problem with my email system!
...having found your service by chance, we've been completely happy and pretty surprised actually. You offer a lot of features, with a very reasonable & logical rate system. ...How much your service will help is possibly beyond your understanding, but I'm sure you've heard that from other people using your service.
I would like to say that your service is unbeatable compared to your competitors.