@mk, you're actually being too nice to #SPF: it doesn't even verify the envelope sender beyond the last hop in the delivery path. It (sort of, sometimes...) `facilitates' traceability... but depends on `everyone else' doing work: the people who want to benefit from SPF need SRS all allong both their inbound and outbound delivery paths, and the people who'd need to implement SRS aren't the ones who benefit from SPF.