back in the mid to thousands. I had a working example of a sender pays email environment. it used hash cash embedded in an email message in combination with con

back in the mid to thousands. I had a working example of a sender pays email environment. it used hash cash embedded in an email message in combination with content filtering. it was more of a proof of concept that an actual practical system but if I was going to do it again today I would instead put the postage at the SMTP level as a protocol extension where your reputation from the mail service perspective would tell you how big a Hash cash stamp to create. This model would accommodate inflation and familiarity for generating bigger and smaller stamps. It's an interesting project for anyone that has the time.