As part of a feature upgrade to Outlook.com and OneDrive, Microsoft is adding security and privacy features to help users protect their synced files and sent emails. These include password protected sharing, optional end-to-end email encryption, attachment encryption, and forwarding-prevention measures.
https://www.notebookcheck.net/Microsoft-brings-new-privacy-and-security-features-to-OneDrive-and-Outlook-com.296558.0.html