Update Search-UnifiedAuditLog.md

Author: dariomws

exchange/exchange-ps/exchange/Search-UnifiedAuditLog.md

@@ -46,6 +46,8 @@ The Search-UnifiedAuditLog cmdlet is available in Exchange Online PowerShell. Yo
 
 If you want to programmatically download data from the Microsoft 365 audit log, we recommend that you use the Microsoft 365 Management Activity API instead of using the Search-UnifiedAuditLog cmdlet in a PowerShell script. The Microsoft 365 Management Activity API is a REST web service that you can use to develop operations, security, and compliance monitoring solutions for your organization. For more information, see [Management Activity API reference](https://docs.microsoft.com/office/office-365-management-api/office-365-management-activity-api-reference).
 
+This cmdlet is also available in Office 365 operated by 21Vianet but it won't provide any result.
+
 You need to be assigned permissions before you can run this cmdlet. Although this topic lists all parameters for the cmdlet, you may not have access to some parameters if they're not included in the permissions assigned to you. To find the permissions required to run any cmdlet or parameter in your organization, see [Find the permissions required to run any Exchange cmdlet](https://docs.microsoft.com/powershell/exchange/find-exchange-cmdlet-permissions).
 
 ## EXAMPLES