Over 1.5 million users have signed up to Microsoft's new Outlook.com, less than 12 hours after it's launch on Monday.

Upon activating its new service, a direct replacement of previous email service Hotmail, Outlook.com officially becomes the world's fastest growing email service, going from 0 to 60 million users in the space of six months.

Since the release of Outlook.com last summer as a preview, millions of people have already actively started using it, yet of the 1.5 million sign ups, most are new users.

Designed to be cleaner, easier to use and focused on connecting users, Microsoft will begin to upgrade every Hotmail user to Outlook.com in the near future.

Current Hotmail users have been encouraged to switch to the new service through a Microsoft email but as with any transition, a large number remain locked into the old service.

Microsoft says the upgrade is seamless and instant for Hotmail customers; everything including their @hotmail.com email address, password, contacts, etc., will stay the same.

For more information, visit Outlook.com

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