Receipts validation

Another issue from 
discussion with an AS4 implementer:

 

If MSH A sends a 
message M to MSH B and B sends a Receipt back to MSH A,  MSH A can 
correlate the messages based on MessageId and RefToMesssageId.   

 

Apart from 
correlation of identifiers, is MSH A also required to validate that the receipt 
indeed matches M?    I.e. for a reception awareness receipt, the 
UserMessage headers should have the values from the correlated 
UserMessage.  For an NRR receipt,  there should be a one-to-one match 
for ds:References and their href and digest values.     

 

If there is such a 
validation and MSH A detects a difference,  which ebMS error is used to 
report this?  

 

Pim