https://www.theregister.co.uk/2018/03/18/windows_10_tests_forcing_use_of_edge_browser_for_links_in_windows_mail/ >Microsoft’s about to test a new feature of Windows 10 that will force users to employ its Edge browser under some circumstances. >Revealed in the announcement of Windows 10 Insider Preview Build 17623 for Skip Ahead, the change means “we will begin testing a change where links clicked on within the Windows Mail app will open in Microsoft Edge”.