A recent update to Microsoft Outlook 2016 has broken some customers connection to the Hosted Exchange. If you have to roll back, Microsoft suggests rolling back to any outlook 2016 version prior to version 1711.
Outlook 2016 for Windows version 1712 and above
Note: You cannot connect Outlook 2010 to MPexchange. You need to upgrade to Outlook 2016. To upgrade, go to https://converge.mp and purchase Office 365 Business (O365STD). If you don't have access to https://converge.mp contact firstname.lastname@example.org
In order to resolve Outlook issues please try the following troubleshooting steps:
1. Close Outlook
2. Clear all related/unnecessary mail related credentials in credential manager.
3. Navigate to the following directory in regedit:
Remove any entries that aren’t ‘mail.aus.exch690.serverdata.net’
4. Download the below .reg file and open on the local machine - this will add the registry entries that are configured to always connect to MPexchange:
Alternatively, navigate to regedit > HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover, choose New DWord 32 and create the following one by one. Give them the corresponding values.
Note: Adding these registry entries will prevent the customers Outlook from connecting to any other hosted provider other than Microsoft hosted exchange. You may need to adjust the records accordingly if the customer wants to add profiles from a different provider other than MPexchange.
5. Additionally, you should back up and removing all files present in the User\AppData\Roaming\Microsoft\Outlook directory.
Once these steps have all been done recreating the Outlook profile should work as expected, assuming a correct autodiscover record.