So, you’ve come up with a HTML email design you’re happy with. Woo! Before you start mailing it out, you’re going to need to test it. There are so many email web apps and desktop clients out there with differing requirements, and ensuring that your newsletter looks great for the overwhelming majority of readers is incredibly important. I use a two-step testing process that includes preliminary testing using a desktop client and a small test group, and final testing using your mailing list web app of choice, such as Mailchimp or Campaign Monitor.