I am trying to configure Postfix to check SPF, and if that passes, then skip the usual greylisting.
It turns out people have asked about this before. Here is Postfix creator Wietse Venema telling Jukka Salmi off in 2007:
and then telling him (again) to read the manual:
So, I have now read access(5) two times, and I still don't understand how I can send "PREPEND X-My-Header: Something" _and_ "OK" from a policy service.
I wonder why he didn't at least also include the answer, besides the railing about reading the manual?
Some more searching turns up this thread from 2008: Multiple responses from a policy daemon, is it possible?, where there conclusion is "No."
Which leaves me slightly confused, and without a solution.