According to industry-leading email service provider e-Dialog, more than 30% of emails are opened on a mobile device. Consequently, if your email content is not fully functional on smaller screens, the weekly newsletter you send out to customers about new catalog offerings, popular sold-out products that are back in stock, and store promotions could result in low response rates, and keep you from capitalizing on wide-open conversion opportunities.

As handheld device usage continues to rapidly penetrate the email space, businesses must begin to extend their mobile optimization initiatives beyond website pages. Email optimization is an integral piece of a successful customer acquisition and retention program.

Source: Responsive Email Design: What Are You Waiting For?