This Warning event indicates that transport pipelining is enabled on a server that has Microsoft Exchange Server 2010 installed. Pipeline tracing is a diagnostic feature that enables you to capture diagnostic information about e-mail messages as they encounter transport and routing agents that are registered on Simple Mail Transfer Protocol (SMTP) events in the transport pipeline.

Pipeline tracing produces significant diagnostic logging and can affect the performance of the Exchange server. If enabled for a long time, pipeline tracing can potentially use a significant amount of disk space. Therefore, pipeline tracing should only be enabled for short periods of time to diagnose or investigate immediate and specific transport agent or routing agent problems.

The diagnostic logging that is produced by pipeline tracing includes all the contents of the message as it is passed through the transport agents and routing agents. Therefore, it's recommended that the pipeline tracing output directory be secured so that only authorized people can access the directory.

No user action is required for this warning if pipeline tracing has been enabled to troubleshoot or investigate an immediate and specific transport agent or routing agent problem. However, remember that pipeline tracing should be left enabled only long enough to gather enough information to help you investigate a current problem. Consider doing one of the following:

• If you no longer need pipeline tracing enabled, disable it by running the following command on the Exchange server on which this warning was generated:
  
  Set-TransportServer <Identity> -PipelineTracingEnabled $False
  
  In this command, replace <Identity> with the name of the Hub Transport server on which you want to disable pipeline tracing. For example:
  
  Set-TransportServer Hub01 -PipelineTracingEnabled $False
  
  
• If pipeline tracing has consumed a significant amount of disk space, you can safely move all the log files that are located in the pipeline tracing log directory to another location. You can determine the location of the pipeline tracing log directory by running the following command:
  
  Get-TransportServer <Identity> | Format-List PipelineTracingPath
  
  In this command, replace <Identity> with the name of the Hub Transport server on which you want to view the location of the pipeline tracing log directory location. For example:
  
  Get-TransportServer Hub01 | Format-List PipelineTracingPath
  
  
• If pipeline tracing should be enabled, monitor available disk space closely to make sure pipeline tracing doesn't consume available disk space. Also, verify that only authorized people can access the pipeline tracing log directory.
  
  

For more information about pipeline tracing, see the following topics:

• Enable Pipeline Tracing
  
  
• Understanding Transport Agents
  
  

If you are not already doing so, consider running the Exchange tools created to help you analyze and troubleshoot your Exchange environment. These tools can help make sure that your configuration aligns with Microsoft best practices. They can also help you identify and resolve performance issues, improve mail flow, and better manage disaster recovery scenarios. To run these tools, go to the Toolbox node of the Exchange Management Console. To learn more about these tools, see Managing Tools in the Toolbox.