Online Web Access and Exchange 2016
Customers using web-based clients will notice a design change beginning with the new Exchange 2016 Online Web Access splash page.
The service migration begins on Thursday, Oct. 20. During the initial migration, you may receive a pop-up on your workstation asking you to allow changes. Please check Don’t ask me about this website again and click Allow so your mail program will accept the new settings.
— October 20, 2016