"Subtask ValidateConfiguration execution failed: Configure Mail Flow" error when you run the Hybrid Configuration wizard

PROBLEM

When you run the Hybrid Configuration wizard to set up a hybrid deployment between your on-premises Exchange Server 2010 Service Pack 3 (SP3) environment and Exchange Online, you receive the following error message:

CAUSE

This issue occurs if hybrid mail flow connectors already exist in the on-premises environment and in Exchange Online.

SOLUTION

Important You will lose mail flow while you perform these steps. To minimize the disruption, perform this procedure during a scheduled downtime.

Remove the hybrid mail flow connectors from the on-premises environment and from Exchange Online. To do this, follow these steps:

1. Remove the Send and Receive connectors from the on-premises environment. To do this, open the Exchange Management Console, and then follow these steps:

   1. To remove the Send connector, expand Organization Configuration, click Hub Transport, click the Send Connectors tab, right-click Outbound to Office 365, and then click Remove.

   2. To remove the Receive connector, expand Server Configuration, click Hub Transport, click the Receive Connectors tab, select the server that has the Receive connector that you want to remove (usually the hybrid server), right-click Inbound from Office 365, and then click Remove.

2. At a command prompt, run the following command to sync all domain controllers:

   repadmin /syncall 

3. Remove the Send and Receive connectors from Exchange Online. To do this, follow these steps:

   1. Sign in to the Office 365 portal, click Admin, and then click Exchange to open the Exchange admin center.

   2. Click mail flow, and then click connectors.

   3. To remove the Send connector, click Hybrid Mail Flow Outbound Connector under Outbound Connectors, and then click Delete ().

   4. To remove the Receive connector, click Hybrid Mail Flow Inbound Connector under Inbound Connectors, and then click Delete ().

4. Do one of the following:

   • To enable centralized mail transport (which routes all Internet-bound messages through your on-premises Exchange servers), connect to Exchange Online using remote PowerShell, and then run the following command

     Set-HybridMailflow -CentralizedTransportEnabled $true 

   • To disable centralized mail transport (which delivers Internet-bound messages directly by using the external recipient's DNS settings), connect to Exchange Online by using remote PowerShell, and then run the following command:

     Set-HybridMailflow -CentralizedTransportEnabled $false 

5. Verify that the values of the TrustedMailOutboundEnabled and TrustedMailInboundEnabled parameters are set correctly on the remote domain. To do this, follow these steps:

   1. In Exchange Online:

      1. Connect to Exchange Online by using remote PowerShell. For more information, see Connect to Exchange Online using remote PowerShell.

      2. Run the following command:

         Get-RemoteDomain Hybrid* | fl Identity,TrustedMailOutboundEnabled,TrustedMailInboundEnabled 

      3. Examine the output. The following is an example of output that shows the correct values for these parameters:

         Identity : Hybrid Domain - contoso.com
         TrustedMailOutboundEnabled : True
         TrustedMailInboundEnabled : False

         Identity : Hybrid Domain - contoso.mail.onmicrosoft.com
         TrustedMailOutboundEnabled : False
         TrustedMailInboundEnabled : True

      4. If the values of the parameters aren't set correctly, use the Set-RemoteDomain cmdlet to set the correct values. For more information, see Set-RemoteDomain.

   2. In on-premises Exchange Server, open the Exchange Management Shell, and then run the following command:

      Get-RemoteDomain Hybrid* | fl Identity,TrustedMailOutboundEnabled,TrustedMailInboundEnabled 

      Examine the output. The following is an example of output that shows the correct values for these parameters:

      Identity : Hybrid Domain - contoso.mail.onmicrosoft.com
      TrustedMailOutboundEnabled : True
      TrustedMailInboundEnabled : False

      Identity : Hybrid Domain - contoso.com
      TrustedMailOutboundEnabled : False
      TrustedMailInboundEnabled : TrueIf the values of the parameters aren't set correctly, use the Set-RemoteDomain cmdlet to set the correct values. For more information, see Set-RemoteDomain.

6. Run the Hybrid Configuration wizard again.

MORE INFORMATION

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