As a digital marketer, testing an email before sending it to thousands of contacts is one of the most important parts of the job. Key to the success of the email is that it is tested for functionality and formatting across all clients it might be opened with.

Different email clients have subtle differences in how they render or display emails, so what might look like a perfectly crafted email in one client might end up as mess of jumbled text in another. These rendering inconsistencies are similar to cross-browser compatibility issues with websites, just slightly worse. However, since the dark ages of Netscape vs. Microsoft, life has become a lot easier for web designers – with Internet Explorer the remaining problem child. It’s no surprise then, that Microsoft Outlook is one of the most temperamental email clients when it comes to email testing.

Email client market share

Let’s take a look at how widely used the different email clients are. According to Litmus the top five email clients in May 2014 were:

  1. Apple iPhone (25%)
  2. Outlook (12%)
  3. Gmail (12%)
  4. Apple iPad (12%)
  5. Yahoo! Mail (11%)

It is interesting to see that most emails are now read on iPhones, while Outlook is still the number one desktop client.

But the picture looks slightly different for the Financial Services Industry. Outlook is also the number one desktop client while the outsider Lotus Notes is still widely used by many of the large fund providers. 72% of financial advisers in the UK and 71% in the US also read their emails on mobile devices, including BlackBerrys.

With the market share divided between so many different desktop and mobile email clients, neglecting one of them means that between 10% to 20% of your audience could see a broken email.

Testing process

Our testing process involves going through a detailed checklist that we complete for every campaign we send. First, we make sure that the email renders as intended in Outlook. We check that the text-only version of the email matches the HTML version and that all links are working and going to the correct destination. At this point we also make sure that the open and click tracking of the email are fully functional.

Once we are happy with the email in Outlook, we look at the big four webmail clients: Gmail, Yahoo, AOL and Outlook.com (formerly Hotmail). If at any point we find any issues, we fix the email and go back and test again in all clients as the newly applied fix might have broken the email in another client.

Lotus Notes is next, and for all the remaining less common clients, we use the excellent online email testing platforms Litmus and Email on Acid. These let you copy and paste in an email’s HTML code and present you with a nice overview of how this code will render in a variety of client versions, both desktop and mobile.

Of course, with responsive emails our testing extends to different devices, such as iPhone, iPad, Android and BlackBerry. Email on Acid and Litmus are also good alternatives for mobile testing if the physical device is unavailable.

Testing is a grueling process, one that needs to be done for every single communication we send, but it’s worth it for an email that will look perfect in every email client out there, be it on desktop or mobile!