Responsive email design ensures that your emails look great on all devices, including desktops, tablets, and smartphones. Use media queries to apply different styles based on the device's screen size. For example:
<style> @media only screen and (max-width: 600px) { .container { width: 100%; } } </style>
In this example, the .container class will take up the full width of the screen on devices with a width of 600px or less.