Office 365 Autodiscover

Outlook 2016 and on wards, outlook client will connect you directly to O365 if there is no auto discover set up. It’s called direct connect. It’s a good feature if the mailbox is on O365 but there are cases where companies are using outlook 2016 / outlook 365 clients but their mailboxes are not O365. So in those scenarios direct connect needs to be disabled.

You can apply the following REG key on PCs to disable direct connect.

HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\office\16.0\outlook\autodiscover
DWORD: ExcludeExplicitO365Endpoint
Value = 1

OR you can apply the above Reg key using the GPO instead.

New-GPO -name “DisableAutodiscover_O365”
Set-GPRegistryValue -name “DisableAutodiscover_O365” -key “HKCU\Software\Microsoft\Office\16.0\Outlook\AutoDiscover” -ValueName ExcludeExplicitO365Endpoint -Value 1 -Type DWORD