If you have a user with Outlook 2016 who are not yet in Office 365 but have mailboxes provisioned in Office 365 you may find Outlook automatically connects to Office 365 and ignores Auto Discover or the on premise Exchange server.
Starting in Outlook 2016 version 16.0.6741.2017, Microsoft enabled a new feature called Direct Connect to Office 365. It was designed to quickly connect Outlook 2016 to Office 365.
A registry key can be added on the PC which will disable the Direct Connect feature and allow either Auto Discover or the On Premise Exchange to configure Outlook.
- Go to Registry Edit on the PC. REGEDIT.MSC
- Go to the following path: HKEY_CURRENT_USERSoftwareMicrosoftOffice16.0OutlookAutoDiscover (I had to create the AutoDiscover Key)
- Create a DWORD: “ExcludeExplicitO365Endpoint” to Value : 1