Although Outlook.com uses some of the same tools -- notably SkyDrive -- as the new Office 2013 suite and the Office 365 subscription plans, Miller saw the new service, like its predecessor, as getting little traction in any but the very smallest businesses.

The Office 365 plans slated to debut later this year or early in 2013, for example, all come with the Outlook email client -- not to be confused with Outlook.com -- as the primary locale for working with messages and other shared content.

Microsoft did not establish a timetable to retire Hotmail, although it confirmed that at some point those with addresses ending in hotmail.com will be forced to use the new Outlook.com interface.

Miller predicted what he thought was a fast move. "Hotmail will continue for time X, whatever X is, but I give it two more years," he said. Within 18 to 24 months, Microsoft will again have a single free online email service.

Users with current Microsoft-provided email addresses and accounts, hotmail.com, live.com and msn.com will automatically be shown the new interface, but can switch back to the traditional look-and-feel if they're dissatisfied.