If you are using a Hosting Australia Hosted Exchange service, there is sometimes a conflict between Office 365 and the Hosted Exchange autodiscovery.
The symptoms are:
- Incessant pop up of password box
- Perhaps a mention of a weird numerical email account
Essentially, the cause is that O365 overrides all other autodiscovery information and tries to connect the server directly to O365.
Starting in Outlook 2016 version 16.0.6741.2017, Microsoft has enabled a new feature called Direct Connect to Office 365. What this feature does is connect Outlook directly to Office 365 if Autodiscover is not working. This may cause your mailbox to connect to Office 365 rather than your on premise Exchange, even with a valid autodiscover record.
For Direct Connect to take effect the user must have an active mailbox on Office 365 with a valid license.
You can stop Outlook from checking Office 365 for settings by setting a registry key:
HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\office\16.0\outlook\autodiscover
DWORD: ExcludeExplicitO365Endpoint
Value = 1
Then restart your computer and it should stop trying to connect to Office 365.
