They are not the first or the last. You CAN have "at most once" processing, since there is always the option of processing zero messages due to systems being d

They are not the first or the last. You CAN have "at most once" processing, since there is always the option of processing zero messages due to systems being down, but it's a joint effort, nobody is able to offer it "for free" (as in, no effort to implement it)