Microsoft's support for the weak security protocol TLS 1.0/1.1* will be removed as of 31 Oct 2018. Devices must therefore support TLS 1.2 or later to connect to Office 365 services to avoid connection issues. 

Your Preparation 
You may

1.  ensure your operating system (OS) and browsers stay at least 
   1. Windows 7 with patch KB3140245, Win 8.1 or Win 10 + IE11  
   2. Mac OS 10.9 + Safari 9 
   3. Android 5.0  
   4. Current version of common web browsers e.g. Chrome, Firefox 

   OR

2. conduct a test at SSL Labs (https://www.ssllabs.com/ssltest/viewMyClient.html) to ensure you are good to go with "Your user agent supports TLS 1.2" at "Protocol Support". 

Reference 

• ITSC Homepage: 
  https://www.itsc.cuhk.edu.hk/it-announcement/general-notices/2018/882-office365-180928 
• Microsoft Updates on TLS 1.0/1.1 Support in Office 365:  
  https://support.microsoft.com/en-us/help/4057306/preparing-for-tls-1-2-in-office-365

Enquiries 

• Department IT Support (For Staff only) 
• ITSC Service Desk 
  • Web: http://servicedesk.itsc.cuhk.edu.hk
  • Phone: 3943 8845 (Office Hours) 

*Transport Layer Security aka TLS protocol provides communications security over a network.