Are you selling or marketing in your responses? If you're selling then you're giving up too much information. Selling, by the way, should only be done on a sales floor. Marketing is spiking curiosity to push people to the next step. It is a tough transition if you come out of sales, but a sales person who gives too much information or "talks himself out of a deal" is exactly what you don't want in an Internet department.
Very simple lead response formula:
2 sentences of response + 1 question at the end that can't be answered with a yes/no = more responses and higher gross
Approach email responses as marketing and stop selling!