Microsoft is currently testing a premium version of its Outlook.com email service. ZDNet reports that the new service is currently named Outlook.com Premium, and that the software maker is piloting the service with a limited number of users. While Microsoft removed custom domain support in Outlook.com in 2014, it's a feature that's part of the new Premium test service.

Microsoft has confirmed the existence of the test, noting that "it is an experiment that we are piloting," according to a spokesperson. "We're always investigating new features based on the wants and needs of our users, and we have nothing more to share at this time."

A new Outlook.com started rolling out to existing users this week, and the backend of the service is migrating over to Office 365 as a result. This enables new features like add-ins, and could pave the wave for Microsoft's custom domain support if the Premium test is successful. Microsoft says it's currently "evaluating interest" in custom domains for Outlook.com, and it's "evaluating the appeal of custom domains but with Microsoft managing the processes of procuring the domain."