So no matter what you do Office 365 exchange won’t connect to outlook.

Here are a few tips that have helped us.

Using Outlook 2007? Forget it move them to a newer version.

Outlook 2010 ? You just need a service pack.

 

Service Pack 2 for Microsoft Office 2010 (KB2687455) 32-Bit Edition

https://www.microsoft.com/en-us/download/details.aspx?id=39667

This will fix 90% of issue with outlook 2010 prompting for a password over and over again even though you have it right

Manually configure Office 365 

https://oit.colorado.edu/tutorial/office-365-outlook-windows-manual-exchange-configuration

 

Turn off IPv6 on your router. 

No really. On the Telstra Netgear 7610 routers, there is a known issue where office 365 will not do the first time authentication without disabling IPv6 on the router.

Outlook 2016 

Create a new mail profile. Hit cancel make the Outlook profile without any details, then connect exchange from within outlook 2016, not using the mail app.

Use 9.9.9.9 DNS and flush the DNS using ipconfig /flushdns

Delete all the old saved credentials in your user profile vault.

 

Remove the Primary Account from Outlook – Great article from Diane Poremsky

https://www.slipstick.com/exchange/primary-account-removed-outlook-2010/ 

In Outlook 2016, the profile key is at:
HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\Profiles\profile-name

In Outlook 2013, the profile key is at:
HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Profiles\profile-name

To remove the Outlook 2010 primary account from the registry, go to the profile key:
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\Current Version\Windows Messaging SubSystem\Profile\profile-name

Export the profile key then search for and remove one (or both) of the registry keys related to primary account.

Searched the profile for 001f662b (or 001f6641 in Outlook 2016)