Email marketing is both an art and a science. The art comes in with elegant designs, punchy subject lines and well-written copy. Then there’s the science. The data and statistics prove which parts of the art gets people to interact with your email… and which parts don’t work as well. That’s where A/B testing comes into play. Running head-to-head tests allows you to experiment with the creative and understand the effect. Read on to understand the rules of A/B testing, the parts of an email you can test and the metrics you should look at afterwards.