Secton 5.1.6 states that "If an AS4 user message is to be encrypted and the user-specified payload data is to be packaged in the SOAP Body, AS4 MSH implementations are REQUIRED to encrypt the SOAP Body."

This applies to situations where the SOAP Body is non-empty, i.e. that there is an XML payload to encrypt. But this is not always the case, in particular when using compression.

We had two vendors having (interop or other) issues with encryption and empty bodies, so some clarification seems to be needed.