REG ADD 'HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover' /v 'ExcludeExplicitO365Endpoint' /t REG_DWORD /d 1 REG ADD 'HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover' /v 'ExcludeHttpsRootDomain' /t REG_DWORD /d 1 REG ADD 'HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover' /v 'ExcludeHttpsAutoDiscoverDomain' /t REG_DWORD /d 1 What worked for us was creating batch files to switch these various options on and off and trying different combinations. We've managed to botch a solution by trying various suggestions from other forums. We'd put it down to using CloudFlare as you could see errors in the cloudflare logs to do with the outlook autodiscovery being blocked but we were unable to resolve them within CF. We've had this issue on and off since we began using Office365. We use Office365 (Exchange Online) to host our email and the staff use Outlook 2016.
