Traditionally the main email clients to target were the main webmail services plus different Outlook versions. - Hotmail - Yahoo! Mail - Gmail - Outlook 2003, Outlook 2007 and Outlook 2010 In 2014 this is radically different – you also need to think really seriously about how emails will render on different mobile platforms. Get the full story at Litmus Read also "Which email clients should we design and test for? 2014 update" at Smart Insights