Speed and performance are prioritized, resulting in an excellent browsing experience for everyone. Here are the most common code tweaks that I’ve found necessary during this test phase: Sometimes, a switch from percentage widths to fixed widths is needed. Some people open emails weeks or months later, the same way people use bookmarks to return to web sites. Be sure all your images use the alt, height, and width attributes. When your HTML email is viewed with a device (or web browser horizontally re-sized) less than 480 pixels, these definitions will activate.