I built and sent 3-4 thematic newsletters to over 8 million subscribers every week that were major sources of revenue for Indiegogo. To further improve email performance, we invested over 4 months to A/B test variables such as subject line, number of featured campaigns, image size, calls to action (both copy & color), price vs. no price, copy vs. no copy, UI design, and much more. What came out of this aggressive testing was a huge redesign of our newsletter template. Results showed that subscribers prefer the most pared down option: large high-resolution images and no price and copy. There was an 87% lift in click-through rate, a 118% increase in value per subscriber, and a 53% increase in the percentage of revenue brought in by newsletter emails in a single quarter. Here are examples of four iterations I coded and tracked using our ESP.