Which email clients should you be testing?

We all know the importance of varying copy and creative for different audience segments, along with the value in testing alternative versions to see what performs best.

But many people often overlook the devices people use to view their emails. Some people have yet to use a responsive design and others use a template that is not sufficiently adaptive to mobile.

This analysis from Litmus Labs lists the most popular devices used, based on 321 million email opens in December 2013 as measured via their Analytics tool.

If your email marketing designs are not responsive or adaptive to mobile, this graphic might make you switch….