For those who complain about spam but don't use what we offer, I've been looking at how effective our SMTP-time measures are, and I'm quite impressed. Almost 70% of all mail targeted at our Exim gateways gets thrown out during the SMTP session proper. The largest part by far because the senders are on one of the DNS blacklists. This is directly followed by messages that are refused because the recipient doesn't verify. Illegal HELO with IP addresses or other rubbish come next, and failed sender verification and protocol violations follow suit.