The move has marked the end of the once-mighty free email service.
Microsoft in a blog post said Outlook.com now has more than 400 million active users after the migration, which took about six weeks to complete.
According to the New York Daily News, Microsoft transferred more 150 million gigabytes of data during the upgrade.
The webpage Hotmail.com now redirects to Outlook.com. Microsoft said users don't have to update the settings on their smartphones, and they can keep their '@hotmail.com' email addresses.
Hotmail dates all the way back to 1996. Microsoft acquired what was then known as "HoTMaiL" in 1997.
It was rebranded as MSN Hotmail, and became a rival of AOL and Yahoo. Google's Gmail service is now seen as Outlook.com's main competitor, the report added.
--ANI (Posted on 04-05-2013)