Email Client Popularity

RNM recently sent our a Xmas greetings and end of year shut-down notice to our clients and prospects. As ever we monitor the open rates, click-throughs and other recipient behaviour on these emails.
One interesting statistic is which email clients recipients prefer to use.

The example illustrates clearly the hegemony of Outlook in all it's versions however interestingly the iPhone is the second most popular email client. Surprised?