Response Insights is a BETA feature that offers data-backed suggestions to improve the predicted reply rates of your email messages. You can learn more about the algorithm here.  

To estimate how effective your email is, click on the "Insights" tab of the Yesware Sidebar within your compose window. Here, you will be able to view your email grade and determine what could be improved upon by clicking the "Get Insights for this Email" button at the bottom of the Sidebar. Click on each category to learn more information about what makes a great email, and make sure to pay attention to the "Spam words detected" flag.