The iPhone dominates with an email open rate for retail of 17.9 percent. However, the rates for both the iPad and Android devices are growing quickly, with the iPad posting a 7.13 percent open rate in the second half and Android 3.61 percent.

“The big news for retailers is that about 28 percent of their audience is consuming email campaign content on a mobile device,” said Patti Renner, director of marketing at Knotice, Akron, OH. “That’s a 40 percent increase in just six months and the numbers continue to rise.

“Even if you resist optimizing your email for mobile, or choose to stay with an email provider who doesn’t have the ability to manage mobile optimization of email appropriately, you’re still messaging across the mobile channel, like it or not,” she said. “You simply can’t avoid it – it’s the consumer preference.”

iPad opens jump
During the second half of 2011, there was steady growth in mobile email open rates across industries, with 27.39 percent of all emails opened on a mobile device, an increase of 36 percent from the first half of the year.

However, the retail industry was unique in a couple of ways, including a 91 percent increase in the use of iPads to view email in just six months. While retailers may be tempted to optimize for mobile with only the iPhone in mind, the numbers suggest they may want to consider the iPad and Android devices as well.

Another way that the retail industry is unique when it comes to mobile email is that the click activity tends to remain steady throughout the entire day for retail campaigns.

“It shows that people are taking a break from playing Angry Birds to read email, and it also means marketers need to incorporate tablets in their strategy if they aren’t doing so already,” Ms. Renner said.

“Where other industries had sharp peaks in CTO activity and mobile open rates, the retail audience was engaged on a steady basis, day and night,” she said.

Time to prepare
Knotice points out that some devices may have stronger open rates than the numbers suggest since only the iPhone automatically downloads email images, which is how email opens are measured. On Android, opens are not recorded unless “show images” is activated in the email.

When it comes to mobile email click-to-open rates, or the ratio of unique clicks as a percentage of unique opens, overall rates are fairly even between smartphones and tablets during most of the workday, with a slight edge given to tablet activity. After the workday, mobile email click-to-open rates gradually increase beginning at 8 p.m. and peaking at 1 a.m.

Despite the growth in email open rates, the numbers show that the majority of email clicks are still occurring on desktop devices. In retail, the percent of email clicks occurring on smartphones was 12.29 percent, on tablets 4.41 percent and on desktop, 83.29 percent.

“While some marketers continue to rationalize and hope their customers love them so much that they’ll save their email to read for later on desktop if their email experience on mobile fails, our data confirms that’s clearly not happening within the retail space,” Ms. Renner said. “Mobile is becoming an increasingly important channel – tablet use is on the rise – and it’s important to prepare and deliver campaigns designed around the channel your customers prefer.”