From the moment your campaign is launched you can start monitoring live data on it's progress from the reports area of your account. These reports show trends that let you assess performance and optimise the effectiveness of future campaigns. Included in these reports are a snapshot overview and the ability to compare with previous campaigns.
You can even track your email's effectiveness at bringing traffic to your website through Google Analytics. You'll be able to chart the navigation path of visitors through your site who arrived via your email, and obtain the conversion rate of sales and inquires as a direct result when correctly configured. In this way you can acurately determine the return on investment for each camapign you launch.
Continue reading about the type of reports and data available: