The best idea so far that I have on this will depend on the price of your product. Obviously if its a high price, high value, high ticket item then it may make sense to actually schedule a physical meeting or an online meeting with software such as go to webinar or go to meeting for example. And then go over your proposal live with your customer. If at all possible in your case, this will be the best possible scenario. What I found over the years is people have all sorts of different reasons why they dont email back and why they dont call back. You can never know what type of objections they might have before you call them. This method doesnt cost that much extra but allows you to close much more deals than when you actually email them. So to recap do not send them proposal, schedule a meeting to review the proposal instead. When you review the proposal, show it to them and give it to them as well.