Experts at the IT Department of the EU parliament bans the Microsoft mobile Outlook app due to the recently disclosed privacy and security issues. The EU Parliament fears that members credentials could be exposed to a third party. Microsoft refused any claim that the service used credentials were double-encrypted using a server per-account unique key and a client device unique key. Microsoft spokesman explained that if customers have concerns though, they can follow guidance on Controlling Device Access on Microsoft TechNet to block the app and continue using the Outlook Web Access (OWA)”]
Source: https://securityaffairs.co/wordpress/33502/intelligence/eu-parliament-bans-mobile-outlook-app.html