Outlook.com has left beta testing, and Microsoft has made the Web app open to the public.

During the beta test, the app racked up 60 million users, and nearly 20 million of those were swiped from Gmail. Users cited integration with Office Web Apps and SkyDrive as top reasons for switching over.

Microsoft is riding the momentum by launching a $30 million ad campaign, part of which will accuse Google (News - Alert) of snooping through e-mail to craft ads for users.

Outlook.com also allows users to send an amazing 300 MB worth of e-mail attachments. The next largest competitor only allows 25 MB worth of attachments.

Microsoft brags that users see 60 percent fewer ads when using Outlook.com. Instead of viewing ads, users see Facebook (News - Alert) and Twitter updates from the person who sent them an e-mail.

By this summer, all of Hotmail will transition to Outlook.com, although Microsoft (News - Alert) won’t be retiring the Hotmail domain. Users can keep their Hotmail address, and folders, contacts and passwords should migrate to Outlook.com without a hitch.

After logging into Hotmail, users can find a link that says “You @ Outlook” in the bottom right corner of their home screens. A press of the link migrates Hotmail over instantly.

In addition to the ability to send 300 MB attachments, users will notice that contacts in Outlook.com will automatically update when information changes on Facebook, Twitter (News - Alert) or LinkedIn.

“We are trying to push people who have gotten lazy and comfortable with an email service that may not be all that great and help show them what email can really do for them,” said Outlook.com senior director Dharmesh Mehta.

According to ComScore, Gmail had 306 million users (not counting mobile) through last December, an increase of 21 percent over the previous year. Yahoo came in second at 293 million while Hotmail trailed behind at 267 million.