Not sure what rulesets you're referring to. I understand the spam prevention techniques (DKIM, SPF) but those are all widely accessible open standards. Could you give an example of the barriers to entry that you mentioned?
Try setting up your own email server and you'll see. There were even a few horror comments on HN from people owning domains for 15+ years with stellar security email servers setup + DKIM + SPF whose emails are going straight into spam.
