The Exchange Mail Flow Troubleshooter tool helps provide easy access to various data sources that are required to troubleshoot problems with mail flow, such as non-delivery reports, queue backups, and slow deliveries. The tool will then automatically diagnose the retrieved data, present you with an analysis of the possible root causes, and suggest corrective actions. For more information about the Exchange Mail Flow Troubleshooter tool, see Microsoft Exchange Analyzers.

For more information about how to troubleshoot message failures, see the following topics:

• Troubleshooting Message Delivery Failures in Exchange 2007
  
  
• Troubleshooting Mail Flow Issues due to Mailbox Logon Failure
  
  
• Troubleshooting Mail Flow from Exchange Server 2007 to Exchange 2000 or Exchange 2003 in the Same Organization
  
  
• Unable to Receive External E-mail and the StartTLS Verb Is Not Advertised in Exchange 2007
  
  

Exchange 2007 uses certificates for much of its transport authentication and encryption functionality. Specifically, various implementations of Transport Layer Security (TLS) are used by the Microsoft Exchange Transport service to help secure session communication between transport servers. For more information about how to troubleshoot certificate issues, see the following topics:

• Certificate and Authentication Issues
  
  
• How to Troubleshoot STARTTLS Certificate Error 12014
  
  
• How to Troubleshoot Direct Trust Certificate Errors 1037 and 2019
  
  

The routing of a message determines the type of queue in which a message is stored. Exchange 2007 uses the following types of queues: Submission, Mailbox Delivery, Remote Delivery, Poison Message, and Unreachable. For more information about these queues, see Managing Queues.

When you're troubleshooting message delivery issues, the Unreachable queue is often a good starting point. The Unreachable queue is a persistent queue that contains messages that cannot be routed to their destinations. Regardless of destination, all messages that have unreachable recipients reside in this queue. The messages remain in the Unreachable queue until they expire or until the administrator resubmits the messages to the categorizer. For more information about how to troubleshoot messages in the Unreachable queue and other queue issues, see the following topics:

• Troubleshooting MSExchangeTransport Service Events
  
  
• Troubleshooting Outbound Mail That is Put in the Unreachable Queue on the Hub Transport Server
  
  
• Troubleshooting Message Delivery Failures in Exchange 2007
  
  
• Troubleshooting Mail Flow Between Exchange 2003 or Exchange 2000 Servers and an Exchange 2007 Hub Transport Server
  
  
• Messages Queue on an Edge Transport Server with 500 5.1.1 Unrecognized Command Error
  
  
• Troubleshooting Mail Queues That Are Increasing on Edge Transport Servers
  
  
• Troubleshooting Edge Transport Server Queues That Contain Mail Destined to a Hub Transport Server
  
  
• Event Similar to Event ID 9514 May Be Logged in the Application Log
  
  

Non-delivery reports (NDRs) are a type of delivery status notification. NDRs are generated whenever a message can't be delivered. If a server detects the reason for the delivery failure, it associates the reason to a status code and a corresponding error message is written. For more information about how to troubleshoot NDR issues, see the following topics:

• Non-Delivery Report Issues
  
  
• Understanding Non-Delivery Reports
  
  
• How to Copy NDRs to a Mailbox
  
  
• How to Troubleshoot a 5.2.1 NDR When Users Send Messages to a Public Folder
  
  
• Incoming Messages to Edge Server Fail with 550 5.7.1 NDR
  
  
• What to Do If Your Organization's IP Address is Blocked By Another Exchange 2007 Organization
  
  

For information about how to troubleshoot issues that cause messages to be unreadable, see the following topics:

• A Message Is Formatted Incorrectly and Cannot Be Read When a Foreign Language Disclaimer Is Appended by the Hub Transport Server
  
  
• A Signed or Sealed E-Mail Message That Is Sent Outside the Organization Is Wrapped in a Disclaimer Message and Cannot Be Read by the Recipient
  
  

Pipeline tracing is a diagnostic feature in Exchange 2007 that enables you to capture diagnostic information about e-mail messages as they encounter transport agents registered on Simple Mail Transfer Protocol (SMTP) events in the transport pipeline. Microsoft Exchange captures verbose information about the changes that each transport agent applies to messages in the transport pipeline in message snapshot files. For more information, see Using Pipeline Tracing to Diagnose Transport Agent Problems.