More than 1 million people signed up for Microsoft's Outlook.com in the first six hours the company's new online email service was available.
Microsoft is hoping that Outlook.com, the eventual replacement for its Hotmail personal email service, will help it better compete against rival email service providers Yahoo and Google.
Launched Tuesday, Outlook.com boasts a streamlined, Metro-like interface, and links to social networking sites like Facebook and Twitter. The service is integrated with Microsoft's Office Web Apps and provides a way to store and share documents through Microsoft's SkyDrive file hosting service.
Outlook.com also offers new tools for managing spam and junk mail, including the ability to detect mass-marketing messages and file them in separate folders.
Outlook.com is technically still in "preview" stage and Microsoft is reportedly working on additional capabilities such as a built-in Skype video-calling service and new calendar features. The company hasn't said when the final version will be ready.
Microsoft revealed the 1 million sign-ups in a tweet late Tuesday.
Outlook.com isn't immediately replacing Hotmail, which has some 324 million active accounts worldwide, although that's the long-term plan. Hotmail users are being given the opportunity to switch to the new email system when they log in.
Hotmail, one of the first email services, was founded in 1996 by a startup and acquired by Microsoft in 1997 for a reported $US400 million.