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This parameter is available only in on-premises Exchange.
The GlobalWebDistributionEnabled parameter specifies whether all OAB virtual directories in the organization can accept requests to download the OAB. These locations are advertised by the Autodiscover service. Valid values are:
$true: Any OAB virtual directory in the organization can accept requests to download the OAB. You can't use this setting with the VirtualDirectories parameter.
$false: Only the OAB virtual directories that are specified by the VirtualDirectories parameter accept requests to download the OAB. This is the default value.
In Exchange 2013 CU7 or later, we recommend that you use the value $true for this parameter. The Client Access services on any Mailbox server can proxy incoming OAB download requests to the correct location.