There is no support for Exchange 2003 in the Splunk App for Microsoft Exchange.
If you want to bring in the Message Tracking logs, then be aware that the message tracking logs are incomplete. Specifically, messages that originate and end on the same message store are never recorded. However, they are in the same general format as the message tracking logs for Exchange 2007 and 2010 - just different positions for the fields. Take a look in the props.conf / transforms.conf of the Splunk App for Microsoft Exchange to see an example of how to do it, then look at the first 5-6 lines of a typical message tracking log and match up the field names. This will provide you with an extraction.
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