Just before Thanksgiving here in the U.S., a Microsoft blog post accidentally leaked the company’s intention to buy mobile email application Acompli. Though the blog post itself was pulled down, the URL still revealed the forthcoming acquisition. Today, the two companies are officially confirming the news, with the Acompli team of around two dozen joining Microsoft as a part of a $200 million+ deal.

Recode was first to report the $200 million figure, and we’ve also confirmed. We’ve also heard this was an all-cash deal.

“18 months ago we started building a team and a product around the idea that we could make mobile email better,” reads an Acompli blog post announcing the news. “Today that journey continues as part of a larger organization with the technology, talent, and market reach that will help us take the vision of Acompli to hundreds of millions of mobile users across the world.”

Acompli was backed by $7.3 million from Redpoint and others for its mobile email app designed for a professional user base who need better tools for managing email, calendaring and file sharing while on the go. Satish Dharmaraj of Repoint writes today that it was a “no-brainer” to fund the team behind Acompli, which includes CEO Javier Soltero, Kevin Henrikson and J. J Zhuang.

At Microsoft, Acompli will work within the Office 365 organization and will function as an independent group building out mobile email products for iOS and Android. Though the app already supported Microsoft Exchange email as well as Office 365 for file access, its integration within the larger organization will open itself to even more opportunities to tie the two businesses and their products together.

What’s interesting, however, is that there are no plans to terminate support for competing email services in the Acompli application. Today, the app supports Exchange, Gmail and Google Apps, iCloud, and Yahoo, for example. And many of Acompli’s earliest users are those who took advantage of Microsoft’s competitors’ products. In other words, that means Microsoft is now in the business of running an email client app that supports business customers who have “gone Google,” so to speak, or who don’t utilize Microsoft’s email (Exchange or Outlook.com/MSN/Hotmail), or its cloud services.

That’s a big shift for the company. It’s hard to imagine the Microsoft of just two years ago making this kind of deal.

Of course, what Microsoft is interested in is the business potential for Acompli. Before talks between the two companies got started, Acompli already had several enterprise pilot programs in the works with Fortune 500 companies. The eventual goal was to put these big businesses on a premium tier, where they would help the startup generate revenue. (It’s currently a free app offering for download on iTunes and Google Play.)

As for how Acompli is being tied into Microsoft going forward, a lot of the details are still being ironed out, including whether it will be rebranded, or sold alongside other Microsoft products as a part of a bundle deal. But Acompli for now is remaining focused on email, not other parts of an online productivity suite. Email will remain the heart of what it does, and its other features like calendaring or file-sharing spin off from that.

Microsoft is paying very close attention to the mobile space, and as this acquisition shows, it’s thinking about how it can compete without isolating itself from the larger ecosystem, as in the past. That’s a huge shift indicting some fresher thinking for the Redmond giant, and not the first of its kind either. Microsoft and Dropbox also recently announced a partnership focused on deeper integrations between the two companies, despite Microsoft owning a direct Dropbox competitor with OneDrive.