I would second this! I really liked this functionality in Base, the CRM we used to use and the one I quite frankly prefer for this reason. The reply rate is not very helpful without complimenting it with # emails delivered, opened, then clicked (if applicable). For example: if the open rate on an email was 20% but we got zero replies back, it would trigger a content change. If we had an email open rate of 10% but 20% reply, our target audience is more granularly defined.