The author designed a modern email template by incorporating strategies like progressive enhancement and using modern tools such as Litmus to ensure compatibility with various desktop clients, web browsers, tablets, smartphones, and high-resolution displays. The design process involved creating a simple layout that was then simplified to make it more personal, adding an author's photo and removing the company logo. To address responsiveness issues, the author used media queries to adjust the layout for screens narrower than 780 pixels and smaller screens like smartphones, reducing whitespace and adjusting image sizes. High-resolution displays were addressed by creating images twice as big and downsizing them with width and height attributes. The author also tested emails using tools such as Direct Mail and Litmus, which provided real-time testing and debugging capabilities, and gathered data on recipient engagement through Litmus Analytics.