Troubleshooting Exchange 2007 Email Transport issues using Pipeline Tracing:

Pipeline tracing is a very handy feature for Email Administrators introduced in MS-Exchange 2007. After enabling it you can get a detailed log of message routing through Hub Transport or Edge Transport Servers, this helps me many times to isolate transport issues.

Pipeline tracing generates log files only for e-mail messages that are sent from the Simple Mail Transfer Protocol (SMTP) e-mail address that you specify by using the PipelineTracingSenderAddress parameter on the Set-TransportServer cmdlet. Pipeline tracing does not generate log files for messages that are sent from any other e-mail address. The SMTP e-mail address that you specify can be internal or external to your Exchange organization.

To enable it run the following command in EMS:

Set-TransportServer <Identity> -PipelineTracingSenderAddress <SMTPAddress>

For example, to configure the SMTP address, abc@contoso.com, as the pipeline tracing sender address on the Server1 computer, run the following command in EMS:

Set-TransportServer Server1 -PipelineTracingSenderAddress abc@contoso.com

Once enabled then try sending email using the above email address it will generate the whole transport log in C:\Program Files\Microsoft\Exchange Server\TransportRoles\Logs\PipelineTracing by default, you can find this folder on Exchange Server. You can change the default path using this command in EMS:

Set-TransportServer <Identity> -PipelineTracingPath <LocalFilePath>

For example, to set the location of the pipeline tracing log directory to C:\Pipeline Tracing Logs, run the following command in EMS:

Set-TransportServer Server1 -PipelineTracingPath "C:\Pipeline Tracing Logs"

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