Disable Autodiscover Endpoint Check for Office 365

You can verify this by using the utilities Fiddler or TCPView, keeping track of the attempts to connect to the servers autodiscover-s.outlook.com and outlook.office365.com.

To disable this check, go to the registry key HKEY_CURRENT_USER\Software \Microsoft\Office\16.0\Outlook \AutoDiscover and create a DWORD parameter named ExcludeExplicitO365Endpoint and value 1. Restart Outlook

 

 

You can make changes to the registry with the following command:

reg add HKEY_CURRENT_USER\Software\Microsoft\Office\x.0\Outlook\AutoDiscover /t REG_DWORD /v ExcludeExplicitO365Endpoint /d 1
Or, using the PowerShell cmdlet Set-ItemProperty:
Set-ItemProperty -Path "HKCU:\Software\Microsoft\Office\16.0\Outlook\AutoDiscover" -Name 'ExcludeExplicitO365Endpoint' -Value 1 -Type DWORD –Force