To improve the overall security Microsoft Office 365 will disable support for TLS 1.0 and 1.1.
This means that, starting on March 1, 2018, all client-server and browser-server combinations must use TLS 1.2 or later protocol versions to be able to connect without issues to Office 365 services. This may require certain client-server and browser-server combinations to be updated.
For more infos check the source here.
Update: Microsoft upgraded the documentation including the new date October 31, 2018.
