Which means that the 'processing' in my application has to have the semantics of a serializable transaction. And it might not - as in the very example given in

Which means that the 'processing' in my application has to have the semantics of a serializable transaction. And it might not - as in the very example given in the post, where a processing application sends an email. Hence my complaint that making statements like "our system offers exactly once processing" can be completely correct - from the point of view of the messaging system. But it can be misleading to the casual reader in understanding how it fits into the broader solution, because the messaging system cannot guarantee that my application processes it exactly once. I'm saying the terminology doesn't feel right.