Given the interest, I've started putting together a BCP. It's now posted as
draft-kucherawy-greylisting-bcp; comments welcome. It is only an outline right
now, and I'll fill it in as people make suggestions about topics it should
cover and/or start providing text to include.
It doesn't touch the SMTP extension people are discussing. Someone else can
champion that one if so inclined. It shouldn't go in a BCP because it doesn't
even exist yet. This document will only describe current and historic
practices.
Maybe we can get it on the docket for Taipei. I'll send out some friendly
pings.
-MSK