Your company has a hybrid deployment Office 365. You create a user in Office 365.
The next day, you discover that the new user account fails to appear in the Microsoft Exchange Server on-premises global address list (GAL).
You need to ensure that the user has a mailbox and appears in the Exchange on-premises GAL and the Office 365 GAL.
What should you do?
A.
Assign a Microsoft Exchange Online license to the user account.
B.
From the Microsoft Online Services Directory Synchronization tool, enable rich coexistence.
C.
From the Office 365 portal, modify the sign-in status of the user account.
D.
Delete the user account hosted on Office 365.From the Exchange Management Console, create a new remote mailbox.
Correct, no sync back from O365 to on-prem. So answer D is correct.
https://social.technet.microsoft.com/Forums/office/en-US/3bae8c72-8e4b-4435-a7dc-73e16998dd2d/hybrid-gal-is-not-showing-office-365-users-for-on-premise-users?forum=Exch2016GD