What "same 2 hours" are you talking about? With graylisting, most
legitimate email goes through immediately because it is from a known
source. Most email coming from new sources is spam.
My point was that greylisting will became ineffective as soon as it
became widely used. And so I suggest you to build system, which
does not perturb other hosts.
There may, indeed, be a benefit of rechecking the DNSBLs, DCC,
etc. right before the email is read, but I don't know many people who
do that. I'm guessing that the benefit is fairly small.
It was your point: "After a few hours, other anti-spam tools such as
DNSBLs, RHSBLs, DCC/Pyzor/Razor, etc. have had a chance to react."
TBP