When you try to change or edit some settings of user mailbox by using Exchange Control Panel (ECP) or running Set-Mailbox Exchange Management Shell cmdlet as an administrator, you receive the following warning message:
WARNING: Please update UseDatabaseQuotaDefaults to false in order for mailbox quotas to apply.
Note This issue only occurs in Microsoft Exchange Server 2016 that has cumulative update 5 installed.
This issue occurs because mailbox quota properties aren't handled well.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.