In order to improve the security, Office 365 services are going to stop supporting Transport Layer Security (TLS) 1.0 and 1.1
If you are in hybrid scenarios (either with Exchange or Skype for Business) and/or if you use AD FS for your authentication services, you need to ensure your on-premises services supports TLS 1.2
Starting March 1st, 2018 if you did not upgrade to TLS 1.2, online services will not be accessible.
You can read this article which provides guidance to move to TLS 1.2 https://support.microsoft.com/en-us/help/4057306/preparing-for-tls-1-2-in-office-365
Albandrod's Memory 