That leaves 1.7 billion people checking email on their mobile devices, so it's extra important for marketers to make sure emails look good and function well on mobiles.
However, in most industries, conversions from email are far more frequent on desktops than on mobile devices, according to the data.
That's a big gap for marketers to fill, but progress is being made. In the past three years, emails have become more mobile-friendly, and just 23% of emails are now desktop-centric.
To learn more about how mobile users interact with email, tap or click on the infographic to see a larger version: