As Microsoft continues its attempts to lure users away from Gmail, the firm says that after releasing Internet-based Outlook.com as a preview, millions of people have signed up to the service.

The Redmond giant announced on its blog that it was "humbled" by active users of the email service -- which has grown from none to 60 million users in a six-month span.

Microsoft has taken Outlook.com out of its preview stages and it is now open to the public. In addition, users of Hotmail will be moved over to Outlook by summer automatically -- although you can upgrade at any time -- and you won't be forced to change your email address.

Outlook.com's final release features include the ability to send large files, address books that automatically update, approximately 60 percent fewer advertisements than Hotmail and the option to connect and update through social media sites including Twitter, Facebook and LinkedIn. Accessible via web browser, Outlook.com will work on Windows and Mac-based PCs, as well as Google's Android through a downloadable application.

Introduced in July to try and compete with Google's free Gmail service, Outlook.com is meant to bring together Microsoft's existing domains, including MSN.com and Hotmail, as well as come with a bevy of features to make it a worthy contender against other popular services including Gmail and Yahoo.

Email is often considered an important element in our daily lives, not only due to the expansion of mobile technology, but as a substitute for pen-and-paper communication. Businesses, however, can monetize these services through advertising placements as well as increasing brand awareness, which may make customers want to use other platforms provided by the same firm. Due to this, email service is a lucrative and expanding market -- something many tech giants want a slice of.

However, when money is on the table, it is not all about positive campaigns or offering the best product. Before this announcement was made public, Microsoft launched a campaign titled " Don't Get Scroogled by Gmail ." Designed to mimic Google's distinctive color scheme, the television, print and website campaign intended to lure users away from Gmail by highlighting the practice of tailoring advertisements based on email content. Whereas Google said that the system is based on keywords and is fully automatic, Microsoft still used the tactic to try and sell Outlook's supposed higher regard for user privacy to secure more users.

Perhaps the privacy scare tactics worked. In an interview with Bloomberg, a senior director for Outlook.com, Dharmesh Mehta, said that a third of the 60 million active users on Outlook.com also use Gmail, but have decided to switch to Outlook for their primary free account.

To try and promote the service, Microsoft intends to spend millions on an advertising campaign spanning across television, print, websites, billboards and radio. The firm expects to spend up to $90 million in the three-month campaign.