On Tue, Nov 30, 2004 at 10:43:40AM +0000, Tony Finch wrote:
After further deliberation about source routing and SPF, I have come
around to the conclusion that Frank is to some degree right, and if
you want to use SPF/Sender-ID, you should use source routes.
Source routes require all mail servers to be open relays.
Why?
If a(_at_)a sends mail to b(_at_)b, and if b(_at_)b forwards to c(_at_)c, then
only
c(_at_)c can send a bounce via b(_at_)b towards a(_at_)a(_dot_)
MTA 'b' accepted responsibility for the message. MTA 'b' needs to
deliver it to MTA 'c' because user b(_at_)b wants it to do so. From that
moment on, the conversation is between 'b(_at_)b' and 'c(_at_)c', errors should
go to 'b(_at_)b' who can, if needed, send a bounce to 'a(_at_)a'.
Alex