I have a strange issue with the Outlook 2016 profile on my Windows 10.
After setting up directory synchronization, configure Azure AD Connect (12/12/2017 version - 1.1.654.0) and synchronize my account, Outlook 2016 prompts me "Your mailbox has been temporarily moved on the MS Exchange server. A temporary mailbox exists, but might not have all of your previous data. You can connect to the temporary mailbox or work offline with all of your old data. If you choose to work with your old data you cannot send or receive email messages."
For now, I have an Exchange on-prem which contains my mailbox. I have only one autodiscover which points to my Exchange on-prem. Only one other user had the issue and he creates his profile again, it works.
Well, I found with network analysis, Outlook 2016 (ProPlus) try autodiscover, and if doesn't work, Outlook try Office 365 autodiscover. For example, if my server goes down for minutes and I launch Outlook, Outlook goes to Exchange Online... and I have to recreate another profile.
It is very annoying and counterproductive
I am in the middle of migration, so I have already accounts synchronized.
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 is great feature but a network hiccup 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. Typically Direct Connect would be a neat feature unles you are in the middle of a migration to 365, but a network hiccup could incorrectly connect you to 365 even though you havent completed your migration yet.
During 365 migrations deom Hosted Exchange or On-Premise, we recommend disabling this option from the user computer registry:
You can stop Outlook from checking Office 365 for settings by setting a registry key.
Value = 1
Best Response confirmed by
Bastien Perez (Occasional Contributor)