Is your network connection matching Office 365’s service requirements? Try Microsoft’s Office 365 Network Analysis tool to find out.
To run the tool, be prepared to allow the Java applet to be executed and then enter your Office 365 tenant URL (e.g. yourcompany.onmicrosoft.com).
If you get the notice “Application Blocked by Security Settings”, go to the Java Control Panel and change your security settings from High to Medium and refresh the page. Try it now or read more about Office 365 SpeedTests.