>For instance, what would happen if mail servers provided feedback to >both senders (on a per message basis in the form of NDNs) Well, since 95% of all mail is spam, and all the spam has fake return addresses, you'd increase the amount of bogus NDNs by more than an order of magnitude. No thanks. Incidentally, on a bad day I already get 400,000 NDNs from mail that I didn't send, just from the minority of MTAs that send NDNs in response to spam now. This is not a hypothetical problem. R's, John _______________________________________________ Ietf@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf