This turned out to be a rather long document, and I haven’t had time yet to thoroughly proof read it. So PLEASE let me know if you find any errors or anything that just doesn’t make sense. Also, the appendix containing more verbose reasoning and explanation is TBD. Otherwise, enjoy! https://powerproductsandservices.com/public/mailserver/Spam Control.pdf There's a fair amount of code and other text associated with the greylisting module. Rather than copy/paste from the document, you can also get the files here: https://powerproductsandservices.com/public/mailserver/ Cheers!