I'm sure many of us would appreciate it if you'd update the list in the
future on how well this works at preventing spam. (At least I know I
would.) I've seen mixed reviews about the efficacy of greylisting, and
I'd love to hear first-hand from someone using courier how effective it
I turned off Graylisting for a customer once. It lasted about 4 hours
before they were screaming to turn it back on. The volume of spam went
from one or two in the inbox per day to a handful each hour. It seems
that someone has their number :^(.
The only problem I've had with Graylisting is when the sending server's
default retry is something absurd like 24 hours. Emails from the day
before suddenly show up too late. If there's a way to specifically tell
the sender, "No, really. Try again in 5 minutes!" then I'd like to hear it.