Run Exchange System Manager.

In the console tree, expand Servers, right-click <Server Name>, and then click Properties.

Click the Diagnostics Logging tab.

Under Services, click MSExchangeTransport.

Under Categories, click the category for which you want to configure the logging level:

• Select Routing Engine/Service to troubleshoot routing issues. Increase the logging level for this component if messages are accumulating in the Messages waiting to be routed SMTP queue.
  
• Select Categorizer to troubleshoot problems with address resolution in Active Directory, distribution list expansion, and other categorizer issues. Increase the logging level for this component if messages are accumulating in the Messages awaiting directory lookup SMTP queue.
  
• Select Connection Manager to troubleshoot issues with dial-up and virtual private network connectivity through Connection Manager.
  
• Select Queuing Engine to troubleshoot problems with the queuing engine. Increase the logging level for this component if you are experiencing mail flow problems, and mail is not accumulating in any of the queues.
  
• Select Exchange Store Driver to troubleshoot issues with the Exchange store driver. Increase the logging level for this component if messages are accumulating in the local delivery SMTP queue, the X.400 queues, or if you have problems receiving mail from Exchange 5.x servers or other mail systems.
  
• Select SMTP Protocol to troubleshoot general SMTP issues. Increase the logging level for this component if messages are accumulating in the Remote delivery SMTP queue to determine if SMTP errors are causing the bottleneck.
  
• Select NTFS store driver to troubleshoot issues with the NTFS store driver. Increase the logging level for this category if messages are accumulating in the Queue folder of your SMTP virtual server and are being processed slowly or not being processed at all.
  
• Under Logging level, click None, Minimum, Medium, or Maximum. Click Maximum for troubleshooting purposes.