Connectivity type: this is objective although sometimes would be a guess. Question is, does connectivity type create specific characteristics in an email sender or the ability to differentiate spam and ham senders? I say yes it does and I like the idea of "Connectivity Type" being one of the columns. Network scale: By this I imagine we are talking about how many IPs this company or individual has delegated to him. Or perhaps who controls the rDNS domain, ie cableco.net has 4 million IPs or homehobbyist.guy has 2 IPs. Technical skill: whoa there... I say doesn't belong here. For one thing, if Anthony runs a server at home he's still a hobbyist but hobbyist doesnt' denote skill level. Also this is subjective. To measure it would require having a test people took to determine their skill level. I think we might all agree there are people in high sysadmin positions at least temporarily who don't have high skill. Responsiveness: This would require a 3rd party service to measure, seems rather changeable / subjective and subject to a lot of varied experience and interpretation. Give me one specific automated test for this if possible. When I suggest classification it is not to get into the area of judging performance or ethics - but only to group in ways that make it possible to tune tests appropriately to the specific characteristics of the group - only relevant to outbound email. Thanks again for your comment. What categories do you imagine for Connectivity Type and Network Scale? I like those a lot.