Every month, Litmus, an email marketing testing and analytics software, analyzes and publishes the latest data on email client market share from their system. They've been tracking email opens across a different devices and clients for over four years.

Their research has seen the entire industry changed as mobile opens grew from 8% of email opens in 2011 to 48% at the end of 2014. Desktop opens also decreased from 58% in 2011 to 22% at the end of 2014. Below is their graph on the environment growth over the past four years. 

Litmus recently published their 2014 year-end review of email client market share. 2014 saw a number of key developments in the email marketing ecosystem that led to some major shifts in email client market share and the industry as a whole. One of the biggest changes was that Gmail no longer blocked images by default in 2014. Since email opens are tracking by using an image pixel in the HTML of the email, Gmail had been discounted in the email client market share for a long time. Many people saw a jump in their Gmail openers in 2014 because of this change. 

According to Litmus, this also led to a spike in webmail opens and a dip in mobile opens. “This behavior [of automatically downloading images], combined with a change to the way Gmail manages images in email, meant that all opens in Gmail look like they're coming from the same place — even though some are coming from web browsers and others are coming from mobile apps. All opens from Gmail now fall into the ‘webmail’ category.”

Below are charts showing the environment growth for desktop, mobile, and webmail email opens throughout 2014 and the adjusted environment growth to account for Gmail changes.

Litmus also tracked the top email clients throughout all of 2014. For the most recent email market share data, visit emailclientmarketshare.com. Below, though, is the top ten email clients of 2014. Mail on the iPhone led the pack with 28% of all email opens in 2014. With the iPhone, iPad, and Apple Mail, Apple made up almost 50% of all email opens. Gmail came in second at 16%, and the iPad was third with 12%.

Understanding the industry email client ecosystem and the email client market share of your own programs can be an important component to optimizing your email marketing.

As you can see in Litmus's data above, mobile is overtaking email marketing and having a major impact on email market share. Over 50% of emails in 2014 were opened on a mobile device. How is that impacting your own email marketing? Have you started to measure mobile opens from your own lists or implemented responsive design techniques?

According to our recent 2015 State of Marketing report, 33% of marketers said their emails are read on a mobile device at least 50% of the time. This was only 24% last year. The issue, though, is that 23% of marketers still don't know how many of their subscribers are opening their emails on a mobile device. 

*Note on chart above: due to rounding, totals don't equal 100%. In 2014, we didn't provide a "don't know" option on this question.

In the same research, we also asked marketers on their use of responsive design on their landing pages and emails. We saw a significant growth in responsive design between 2014 and 2015. In our 2014 research, 42% of marketers rarely or never used responsive design in emails. In 2015, only 24% of marketers use responsive design rarely or never. Sixty-eight percent of marketers view responsive design as absolutely critical/very important to building email marketing campaigns.

How are you optimizing your email programs for the mobile shift? If you're part of the 24% who are rarely or never using responsive design in your emails, make it a priority for 2015. You subscribers are showing the importance of mobile engagement with your content, emails, and landing pages. Be sure to take full advantage of those experiences before it's too late.