From the Snowden documents;
July 31, 2012
Microsoft (MS) began encrypting web-based chat with the introduction of the new outlook.com service. This new Secure Socket Layer (SSL) encryption effectively cut off collection of the new service for FAA 702 and likely 12333 (to some degree) for the Intelligence Community (IC). MS, working with the FBI, developed a surveillance capability to deal with the new SSL. These solutions were successfully tested and went live 12 Dec 2012.