AlbertoP Thanks for taking the time to clarify! I know about "ACLableSyncedObjectEnabled" and it's enabled in all my deployments. However, in my opinion Remote Mailboxes should inherit the Organization Config. Or at least provide a parameter to specify if provisioned mailboxes should inherit the setting from the Organization.
Most of the admins I work with, create mailboxes in EAC. So the "ACLableSyncedObjectEnabled" parameter is not set (simply because EAC doesn't set it by default) and admins have to set it in EMS afterwards... I know this could all be scripted (and that's what most admins do), but a configurable default for provisioned mailboxes would be nice. And I know that this won't happen for Exchange Server 2019, but maybe the PG could consider this for vNext...?