In order to find out which domains are most often used by contacts who read your marketing campaigns, DirectIQ offers a Domains 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 Domains at the top of the page to see an opens report by domains.
Here you can review the percentage of openings by different types of domains.
Campaign Reports Overview