How about we add a new option to "all" mechanism, which instead of "?" or
"-", then ISP can declare a percentage, which is the probability that reach
that point in the rule is a forgery???
Your wish is our command. Just use '~' - it says that the connection
is "probably" a forgery. It is called "softfail" in the spec.
Thanks but I wrote "probability" not "probably".
I mean an actual number between 0 and 1.
The owner of the domain, may have the best information about what this number
should be.
It would be much easier for anti-spam to combine that probability with other
factors if the probability were estimated by the owner of the domain, since
each domain will be different depending on several factors, including
demographics, type of business, rate of SMTP AUTH adoption, etc...
Please consider this seriously. I think this will have a very big effect on
the rate of SPF adoption!