The Unified Messaging server failed to receive an incoming call for user “%1” during the call with ID “%2” because a Hub Transport server is currently busy or not available. To correct this error, make sure that there is at least one Hub Transport server installed in the same Active Directory site as the Unified Messaging server and that a Hub Transport server is available.

Details
Product: Exchange
Event ID: 1081
Source: MSExchange Unified Messaging
Version: 8.0
Symbolic Name: TransportUnavailableFailedSubmit
Message: The Unified Messaging server failed to receive an incoming call for user “%1” during the call with ID “%2” because a Hub Transport server is currently busy or not available. To correct this error, make sure that there is at least one Hub Transport server installed in the same Active Directory site as the Unified Messaging server and that a Hub Transport server is available.
   
Explanation

This Warning event indicates that the computer that has the Unified Messaging server role installed was not able to accept any new voice or fax messages destined for the user referenced in the event description. The Unified Messaging (UM) server may respond to the request with message that resembles “Sorry, we can’t take the message right now. Please call back later” before the call is disconnected. By default this warning is logged when there are more than 1,000 message requests pending for the Hub Transport server. Another symptom you may experience when this event occurs is that MSExchange Unified Messaging Event ID 1082 is logged in the Application log.

Event ID 1081 may be caused by one or more of the following:

  • The computer that is running the Hub Transport server role may be too busy processing the message requests submitted by the UM server.

  • A computer that is running the Hub Transport server role cannot be found in the same Active Directory® site as the UM server. The two server roles must be installed in the same Active Directory site.

  • The Microsoft® Exchange Transport Service installed at the Hub Transport server is not running.

  • An SMTP receive connector is not created or configured correctly at the Hub Transport server.

   
User Action

To resolve this warning, do one or more of the following:

  • If you frequently receive this warning because of a high volume of voice or fax messages, or a high workload at the Hub Transport server, consider adding another Hub Transport server in the same Active Directory site to load balance the requests submitted by the UM server.

  • Make sure that there is at least one Hub Transport server installed in the same Active Directory site as the UM server.

  • Make sure that the Microsoft Exchange Transport service is enabled and running on the Hub Transport server.

  • Make sure than an SMTP receive connector is created on the Hub Transport server. Consider the following when you configure the SMTP receive connector:

    • It should be configured to accept messages from the UM server.

    • It should be configured to use at least Transport Layer Security (TLS).

    • It should have Exchange Server Authentication enabled.

  • Enable SMTP protocol logging to troubleshoot SMTP transport issues. SMTP protocol logging can log the SMTP protocol conversation when UM server submits messages to the Hub Transport server over the SMTP protocol. For more information about SMTP protocol logging, see How to Configure SMTP Protocol Logging.

For more information about the UM message flow, see Overview of the Unified Messaging Message Flow, and Understanding Unified Messaging Incoming Call Handling.

For more information about load balancing and high availability, see High Availability.

If you are not already doing so, consider running the tools that Microsoft Exchange offers to help administrators analyze and troubleshoot their Exchange environment. These tools can help you make sure that your configuration is in line with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. Go to the Toolbox node of the Exchange Management Console to run these tools now. For more information about these tools, see Toolbox in the Exchange Server 2007 Help.

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