According to the Outlook.com Premium preview page, there will be a special offer price of $19.95 per year for the first year the service is available. The regular price will be $49.99 per year once the service is publicly available for purchase.
The preview of Outlook.com Premium offers users five personalized email addresses (which can make use of an existing domain users already own); calendar and document sharing; and an ad-free inbox. According to Microsoft's splash page for Outlook.com Premium, the new service is "powered by the new Outlook.com."
For Outlook.com Premium subscribers, a personalized email address with a custom domain is free for the first year, says the frequently asked questions (FAQ) page. Subscriptions to Outlook.com Premium will auto-renew at "then current prices," the FAQ says, and there will be an additional charge per year for a custom domain.
"If you select a new domain during the registration process, Microsoft will buy the domain on your behalf. Microsoft retains ownership of the domain. You can continue to use your personalized email address based on that domain as long as you renew your Outlook.com Premium subscription," says the FAQ.
With the preview, there's no support for auto-forwarding or group creation. Microsoft is advising users who want more than five addresses to look at Outlook 365 Business Essentials, rather than Outlook.com Premium.