In addition to the availability of TLS, Outlook.com has also enabled Perfect Forward Secrecy (PFS) encryption support for sending and receiving mail between email providers, making it more difficult for attackers to decrypt connections.
Matt Thomlinson, VP, Microsoft Trustworthy Computing Security, announced in a blog post on the company's comprehensive engineering effort to strengthen encryption across its networks and services with the goal to provide even greater protection for data across all Microsoft services.
Also, Microsoft Cloud computing service, OneDrive now has PFS encryption support enabled as well. OneDrive customers now automatically get forward secrecy when accessing OneDrive online (https://onedrive.live.com), or via the OneDrive mobile application and sync clients.
As with Outlook.com’s email transfer, this makes it more difficult for attackers to decrypt connections between their systems and OneDrive.