Return Path released some interesting findings from a study on email – particularly, 81% growth in email activity on mobile devices.

While the majority of email is still read from PCs, the leading platform for viewing email is webmail (48%). Desktop email accounts for 36% and mobile for 16%. Outlook is by far the number one desktop choice, according to the report.

One big conclusion of the report, which seem like common sense, yet may still go overlooked all too often, is that if you aren’t paying attention to how your email renders on mobile devices, you’re likely missing out on customers and conversions.

“The art of ‘designing for the small screen’ may prove to be evolving to the art of designing for the reader on the go,” said Return Path Product Manager Bryan Dreller. “While still critical to the email design process, rendering quality itself is still secondary to sending the right message at the right time.”

“With the rise of the iPad and the tablet market, mobile has been redefined,” he said. “According to our study, iPad viewership has grown 15% between October 2010 and March 2011 and we expect to continue to see this percentage grow in the coming months with the recent release of iPad 2. Marketers need to adapt to this change in where and when consumers are accessing email and online content.”

Another thing to take into consideration is the timing of the messages you’re sending. Take a look at the following graph for how day of the week affects where email is viewed:

This information might be particularly helpful if you’re targeting the consumer on the go.

Earlier this month, we looked at a study commissioned by Microsoft, which found that 45% of those surveyed said their use of email at work will most likely increase over the next five years. 51% said it would most likely stay the same. Only 4% thought it would decrease. At home, 35% said it would increase, 55% said it would stay the same, and 6% said it would decrease.