Microsoft is testing a new service called Outlook Premium. Currently, you can only get it if you receive an invite (if you want one, you can request it here). Outlook Premium gives you five personalized email addresses (using a custom domain of your choosing), an ad-free inbox, and improved calendar sharing. For those who have invites, it's free for the first year. Following that, Outlook Premium is priced at $3.99 per month. This may also be launched as a free add-on for Office 365 subscribers at some point in the future, after the testing phase has concluded. Yet if you're...
Source: http://www.gsmarena.com/microsoft_is_testing_outlook_premium_subscription_for_399_per_month-news-17615.php