Jason Rodriguez, writing for A List Apart:
Just like with responsive websites, there are three main components of a responsive email: flexible images, flexible layouts, and media queries.
The only difference between the web and email is in how these three techniques are implemented.
In email design, we have a limited subset of HTML and CSS at our disposal. We can’t rely on properties and values that designers use for responsive sites on the web; margins, floats, and ems don’t work in many email clients. So we have to think of workarounds.
Frankly before this post I considered “responsive” email as something of a lost cause. But there’s a lot of strategic, well explained code examples here that make me want to revisit the emails we regularly send out as part of our day job. At the very least check out Jason’s solution for flexibile images which has a very clean HTML and CSS-based solution.