...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 think you're providing a marvellous service and I'm seriously thinking of swapping one of my larger ezines over to you.
I would like to say that your service is unbeatable compared to your competitors.