You can verify this by using the Fiddler or TCPView tools to monitor the attempts to connect to the and servers. Somewhere in the fall of 2016, an update was released for Outlook 2016 that enabled a mandatory check of the connection endpoint in the Microsoft 365 (Office 365) cloud. Make sure Anonymous Authentication is not selected here.ĭisable Office 365 Autodiscover in Outlook If you have a Microsoft 365 (Office 365) mailbox connected in Outlook, this tab should have an additional field Logon network security.
If you are using GPO administrative templates for MS Office, this setting can be configured with the policy parameter Online Content Options = Do not allow Office to Connect to the Internet under the following GPO section: Administrative Templates -> Microsoft Office 2016 -> Tools | Options | General | Service Options -> Online Content.
