I use a greylist daemon (http://www.x-grey.com/ http://www.x-grey.com/) as a first line filter and it easily stops 50% of spam right there (the spammer will get

I use a greylist daemon (http://www.x-grey.com/ http://www.x-grey.com/) as a first line filter and it easily stops 50% of spam right there (the spammer will get a transient delivery error---most don't even bother with trying again). Last year I did look into using some realtime black lists, but there were a few critical false positives that kept me from using them (and there's quite a few not worth using---details http://boston.conman.org/2015/05/11.1 http://boston.conman.org/2015/05/11.1).