In order to find out which email clients are most often used by contacts who read your marketing campaigns, DirectIQ offers an Email Clients report.
Go to Campaigns -> Campaigns List, select the campaign that has already been sent and click Reports at the right of the campaign card.
An Overview page with campaign detailed information open. Click Email Clients at the top of the page to see an opens report by email clients.
Here you can review the number and percentage of openings by different types of mobile, desktop and web email clients.