And why not using the existing authentication protocol
on outgoing smtp
server ? So the sender can use the smtp server of the provider of its
email address from any network and SPF can work without any problem.
How would this solve the forwarding problem?
And how are you going to teach everybody to stop doing something that
has been working fine for years?
Just have a look at
http://old.openspf.org/srspng.html
Yieks!