This document discusses responsive email design and the need for emails to adapt to different devices. It notes that 47% of email opens are on mobile devices and 80% of people delete emails that do not look good on their device. It introduces responsive design techniques like fluid layouts and media queries to style emails differently depending on screen width. It provides examples of CSS rules to make navigation, fonts, colors, padding and content responsive. It also lists apps that do and do not support responsive email design.