Could you please provide more information about your environment? Is your environment a cloud only or a hybrid one?
I fould some similar issue that unable to setup Office 365 mail account on Outlook 2016, you could try the below methods to solve this issue
- Use the SARA tool to help you check and recover your outlook issue, download here: https://www.microsoft.com/en-us/download/100607
- Sometimes disable IPv6 will be able to resolve this issue as well.
- Modify the Registry key like "ExcludeHttpsAutoDiscoverDomain"=dword:00000001 and 'ExcludeExplicitO365Endpoint'
The discussion in this thread include different ways to solve this problem, you could take a reference: Unable to setup Office 365 mail account on Outlook 2016
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