And, here’s the results. You can, I’m sure, immediately pick out the point where I turned on the greylisting service. It’s not a complete solution – I still get some spam – but you can see from the graph that I’m getting around 1/3 as much inbound mail as I was getting before.
It’s even more pronounced if you look at the month view
Notice that it affects the sent, as well as received, because so much of my outbound email was reject and bounce messages.