Microsoft's Outlook.com email service has broken the 60 million user milestone just six months after launch, with many new users having previously been Gmail devotees, the software giant claimed.
Microsoft revealed the figures as it begins moving the service out of preview mode and upgrading Hotmail users.
"Microsoft will begin automatically upgrading all Hotmail users to Outlook.com expecting to be finished by summer 2013," wrote Microsoft's Steve Wiens on a company blog.
"Outlook.com has achieved more excitement and scale than expected; there are 60 million-plus active users worldwide in a little more than six months of service and it has become the fastest growing email service today.
"Over one third of the new users in the US are upgrading from Gmail, the rest are primarily Hotmail users."
Microsoft reported that over 12 million of the active users are also using the company's Sweep and Schedule clean-up tools to organise their inbox.
The company also claimed over 25 million Outlook.com users have also begun using Microsoft SkyDrive cloud storage service.
The Outlook preview mode was released on 31 July and had reportedly accrued more than one million accounts activated within its first 24 hours active.
Outlook went on to break 10 million users mark within one month of launch.
For a full look at Outlook check on V3's hands-on breakdown of the service.