On average, for one domain that I manage, we get 2500~3000 incoming connections/day. I use smf-grey, smf-spamd, RBL, and I permanently reject all incoming mails that are not valid recipients in the domain. About 10% of the incoming mails are delivered the remaining 90% are rejected. Of the delivered messages, less than 0.8% are spam. All strategies for fighting spam have their advantages and disadvantages. It is not, IMHO, a good idea to rely on a single defense. I'm happy with my setup. And, I've no complaints from the user community.
