Domain mail accounts hosted by USA.NET are similarly protected. I did not know they outsourced it. We went looking for the same thing and instituted one early last year. Working great now. No spam at all with all the setup interface options that matter.
Uptime is good too.
We setup boxes on the major free webmail centers to see how things are. Join the WebTrends Live Affiliate Program designed for ISPs. Increase your revenue by providing customers the stats they want.