How can I use message tracing to diagnose an LMTP delivery failure with a 452 error?

Message tracing involves examining the complete path of an email message from sender to recipient. Look for the point where the delivery fails with the 452 error. Most mail transfer agents (MTAs) provide tools for message tracing. Postfix, for example, has the `postmap` and `postqueue` commands. The trace will reveal which server is returning the error and provide clues about the cause.