There’s no denying that email marketing is still the most effective way to sell online. Given how powerful email is, along with the sheer number of “how to” posts about it, it’s tempting to build your efforts around established best practices or simply use your platforms recommended features. Unfortunately, that approach has failed time and time again. Instead, testing – rigorous, methodical, and data-driven A/B testing – is absolutely essential. But where should you start? To answer that question, I’ve put together this list of 15 A/B tests you can jump into today. First, a quick note … Lots of email testing tools exist and the provider you choose must be able to actually run the tests outlined below. This is especially true for testing content blocks (tests five-eight) and calls-to-action (tests 9-12). Additionally, be sure to preview the provider’s analytics to ensure the results of your A/B tests are easy to read and evaluate. Regardless of the provider you choose, let’s get into the 15 most crucial A/B tests.