Non-repudiation refers to a state of affairs where the purported maker of a statement will not be able to successfully challenge the validity of the statement or contract.
Source: Wikipedia (accessed in April 2013)
DDEX messages convey, in effect, an extension or exhibit to the commercial contract between sender and recipient. It is therefore very important that the sender of a message knows that the message has arrived - and can prove that it has arrived. Equally, it is often important for a company to be able to show that he has not received a specific message. One example where the benefit of having non-repudiatable messages are take-down notices sent from a label to a DSP:
DDEX's message exchange protocols support non-repudiation. When using web-services, non-repudiation is an essential part of the standard. However the FTP profile of the message exchange choreographies do not mandate the use of the acknowledgement messages. And it is these acknowledgement messages that deliver non-repudiation.
DDEX highly encourages implementers of the FTP-based message exchange choreographies to make use of the acknowledgements.