You have an Exchange Server 2010 Edge Transport server.You discover that e-mail delivery to an external SMTP host named Host1 fails.You need to identify which SMTP error codes occur when the delivery to Host1 fails. What should you do？（）

• A、Run the Queue Viewer.
• B、Enable pipeline tracing.
• C、Run the Mail Flow Troubleshooter.
• D、Configure the protocol logging level on the Send connector.