The document discusses how to use an Idempotent Filter in Mule to avoid duplicate messages by checking message IDs. It provides an example of configuring an Idempotent Filter to use a simple-text-file-store to store message IDs in files and check for duplicates. When the example flow is run, it generates a text file to store message IDs and will return "passed" for new messages but "EXCEPTION" for duplicate messages.