The nearly two dozen screenshots posted by cnBeta.com were of Outlook, the email client that's included in Office on both Windows and OS X. cnBeta.com said that the screenshots were taken from a leaked internal test version of the application.

Some long-time Microsoft watchers, including Tom Warren of The Verge, have reported that previews of a new Office for Windows have been circulating among partners and testers. The software that cnBeta.com obtained may have come from a similar early-look program for Office on the Mac.

cnBeta.com's screenshots showed an Outlook more closely aligned with the user interface (UI) of the client in Office 2013, the current edition for Windows, and fit OS X Yosemite's look-and-feel with a "flatter" design.

According to the leaked build, Outlook will still rely on a "ribbon" at the top of the window, a UI feature that debuted in Office for Mac 2011 four years ago to some resistance.

Additionally, the new Outlook will integrate with OS X's Notification Center to show the most-recently-received messages. And, not surprisingly, the suite's applications will be tightly bound to Microsoft's OneDrive cloud-based service for document storage and collaborative work.

An upgrade from Office for Mac 2011 is long overdue: Microsoft shipped that edition in October 2010. The long lag time has implications because 2011's support retirement date -- when the company stops providing security updates -- is Jan. 12, 2016, less than 14 months away.

In the past, Microsoft's OS X development team has talked up upcoming editions, but this cycle there was been only silence from the company. Among the unknowns are a release date, the name of the edition and pricing.

One certainty is that the next Office for Mac will be available to subscribers of Office 365, Microsoft's rent-not-buy program. It's also likely that Microsoft will continue to offer perpetual licenses -- the traditional kind that are paid for once, with rights to use the software as long as the customer wants -- because revenue from the Office 365 subscription model continues to lag far behind the more familiar one-off or volume perpetual licenses.

It's also a good bet that Microsoft will retain the price synchronization of retail Mac licenses with Windows' Office 2013, a move the company made last year when it introduced Office 365. Currently, a single-license Office for Mac Home & Student lists for $139.99, and Home & Business for $219.99, prices identical to the same-named version of Office 2013.

The Office 365 editions of Office for Mac 2011 are equivalent to Home & Business in that they include Outlook, but subscribers can also use Office on tablets, such as Office for iPad.

cnBeta.com also cited "Outlook 16" as the application's formal name, implying Microsoft has skipped a version: Office for Mac 2011's Outlook was pegged v. 14. The v. 16 may indicate that the next Office for OS X will be based on the same code as the next edition for Windows: Office 2013 is formally tagged v. 15. Rumors have also pinned the code name "Office 16" on the upcoming Windows edition.

Office 16, probably named to match Microsoft's convention, may launch as early as the spring of 2015. If that's the case, and Microsoft releases a companion upgrade for the Mac at the same time -- or even earlier -- it would be another departure for the Redmond, Wash. company, which in the past has shipped the OS X version an average of six months after the one for Windows.

On the side of an early appearance of Office for the Mac is the fact that Microsoft shipped a touch-only version for the iPad in March, but has yet to do the same for touch-centric Windows devices, including Microsoft's own Surface.