You can run a test on just about any part of an email, but one of the best things to test is your email subject line. Subject line A/B testing determines which email subject line is most likely to have the highest open rate, and therefore be seen by the most people. You can also test the content within an email to see what generates the most clicks. With Constant Contact’s Ecommerce Pro Plan, our A.I-driven tool does the testing work for you—processing data, continuously A/B testing, and predicting the best outcome.