The example script test_message_decoder.php is ready to be run from the command line taking as argument the message file name.
If you do not specify any message file name or you run as a Web server script, you can change the default message file name in the script itself where it says test/sample/message.eml .
If you are accessing the messages from a POP3 server, you can also check the examples that come with the POP3 class that integrate with the MIME parser class to read messages directly from the server without having to store them in a file first.
phpclasses.org/pop3class