To determine where message delivery failed or where the non-delivery report (NDR) is being generated, perform one or more of the following steps:

1. Use the Mail Flow Troubleshooter tool. The tool provides easy access to various data sources that are required to troubleshoot problems with mail flow, such as NDRs, queue backups, and slow deliveries. The tool then automatically diagnoses the retrieved data, presents an analysis of the possible root causes, and suggests corrective actions. For more information about the Mail Flow Troubleshooter, see Overview: Microsoft Exchange Analyzers.
   
   
2. Use the Queue Viewer on a Hub Transport server or Edge Transport server to determine where message delivery failed. For example, the message may be in a delivery queue that has a status of Retry, or in the Unreachable queue. For more information about the Queue Viewer and message queues, see Managing Queues.
   
   
3. Check the NDR to verify the delivery status notification (DSN) codes, and to determine which server and component are generating the NDR. For more information about DSNs, see Managing Delivery Status Notifications.
   
   

Use the Test-ServiceHealth cmdlet in the Exchange Management Shell to verify that all the required Exchange services are running on the transport server where message delivery failed or on the transport server that generated the NDR. For more information, see Test-ServiceHealth.

Verify that the hard disk drive that holds the message queue database has enough free disk space. By default, the message queue database is stored at <Exchange Installation Drive>\Program Files\Microsoft\ExchangeServer\TransportRoles\data\Queue. This location is controlled by the QueueDatabasePath parameter in the EdgeTransport.exe.config application configuration file.

By default, in the release to manufacturing (RTM) version of Exchange 2007, the hard disk drive that holds the message queue database must have at least 4 GB of free space.

By default, in Exchange 2007 Service Pack 1 (SP1), the hard disk drive that holds the message queue database must have at least 500 MB of free space.

If the free space does not meet the minimum threshold, all mail delivery stops. For more information, see Understanding Back Pressure.

Verify that the necessary connectors are enabled and configured appropriately on the transport server where message delivery failed, or on the transport server that generated the NDR. For more information, see the following topics:

• How to View the Configuration of a Receive Connector
  
  
• How to View the Configuration of a Send Connector
  
  
• How to View the Configuration of a Foreign Connector
  
  

Check Windows Event Viewer to see the events that are in the application event log on the Hub Transport servers, Edge Transport servers, or Mailbox server that are involved in the delivery of the message. You can increase logging levels on the Exchange processes that are generating errors. For more information, see Diagnostic Logging of Exchange Processes.

Check the DSN error codes that are contained in the NDR. The error codes can be useful to help determine the source of the problem. For example, an error code might point to a problem with the domain name system (DNS) service or with network connectivity. For more information about DSN error codes, see Understanding Non-Delivery Reports.

Use Active Directory Service Interfaces (ADSI) Edit to verify that the following list of Active Directory attribute values are correct for the recipient object:

• Legacyexchangedn
  
  
• Homemdb
  
  
• Homemta
  
  
• mailNickname
  
  
• proxyAddresses
  
  
• msExchHomeServerName
  
  
• msExchMailboxSecurityDescriptor
  
  
• msExchMailboxGuid
  
  

  Note:
  You must check the recipient object attribute values on the same global catalog server that is being used by the transport server where message delivery has failed. You can find the global catalog server that is being used by a transport server in the transport server properties in the Exchange Management Console. For more information, see Configuring Transport Server Properties.

Compare the Active Directory attribute values for the recipient object that you obtained in step 7 with the recipient object attributes on the global catalog server that is referenced by the Mailbox server that contains the recipient's mailbox. If any of the values don't match, perform one or more of the following steps:

1. Verify that replication is working between global catalog servers.
   
   

   Note:
   You can use the Nslookup.exe command to test your DNS configuration. DNS configuration problems are frequently the cause of replication problems.

2. If there are any servers that are running Exchange Server 2003 or Exchange 2000 Server in your organization, verify that the appropriate routing group connectors and bridgehead servers are functioning correctly. For more information, see Message Routing in a Coexistence Environment.