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. Please note, this is only available on Gmail.
To estimate how effective your email is, click on the "Get Insights" button in the upper right of your compose window. This will open up the Yesware Sidebar to the Response Insights tab. Here, you will be able to view your email grade and determine what could be improved upon. Click on each category to learn more information about what makes a great email.