The faster you reply to customer questions, the higher the conversions will be as well as the chances for repeat business. If a customer asks about a product, it means that the person is interested in the product, and very likely in the middle of a buying decision. How you react, and critically, how quickly you respond, can be the difference between making a sale or not. Keep your customers informed by notifying them when you have received the order and when it's on the way to them. Also, if things don't go entirely according to plan, they will be understanding as long as they feel that they get honest communication. Even though you may not have any new information, it's better to let them know that you're working on it than not replying at all.