Outlook.com also sorts messages of different types into separate buckets, so that, for example, users can prioritize reading email from contacts over newsletters they're subscribed to.

Outlook.com also includes Office Web Apps, the online versions of Word, Excel, PowerPoint and OneNote, along with the SkyDrive cloud storage service.

Still, Sterling doesn't find the features earth-shattering. "The absence of display ads might lure some people from Yahoo but I don't think there's -- so far -- enough here to gain many converts from Gmail," he said.

Gartner's Matt Cain also found Outlook.com to be less exciting than Microsoft is making it out to be. "There really is no new technology here -- the filtering tools have been around for some time as well as the social network integration," he said via email.

"What is new is the cleaned-up user interface, and the marketing spin, and the tight integration with Office Web Apps and Skydrive, and the forthcoming integration with Skype," Cain added.