"We will access, disclose and preserve personal data, including your content (such as the content of your emails, other private communications or files in private folders), when we have a good faith belief that doing so is necessary to."
And while Microsoft does allow Windows 10 users to opt out of all of the features that might be considered invasions of privacy, users are opted in by default. Rock, Paper, Shotgun explains the opt-out process step by step.
Windows 10 will sync settings and data by default with its servers. That includes browser history, favorites and currently open web pages, as well as saved app, website and mobile hotspot passwords and Wi-Fi network names and passwords.
Activate Cortana, Microsoft's personal virtual assistant, and you are also turning on a host of data sharing, as Microsoft's new privacy statement points out: