On Fri, Feb 13, 2004 at 04:24:28PM +0000, Brian Candler wrote:
The advantage of the callback is that you can say for certain that this
*particular* message must have originated from that ISP, and within a known
timeperiod of a few days. It also guarantees that should the message fail to
be delivered, the bounce would be deliverable.
Plus it's a reasonably useful filtering technique in its own right, which
means there's immediate benefit to you in implementing it even if no-one
else has started using SRS.