I'm noticing that via my Litmus tests, I have an email that was designed to be responsive.

It's responsive in the html but when I put them in Convio, but the 2 column images/text do not stack in mobile devices. And some of the text and images overlapp a little in Android 4.4 and iPhone 5. When you re-size the browser in a desktop email client, it's responsive and it stacks.