Hmm, I didn't mean that all notifications are spam. But, the task recipients face for sifting and sorting their inbox into different buckets is essentially the

Hmm, I didn't mean that all notifications are spam. But, the task recipients face for sifting and sorting their inbox into different buckets is essentially the same faced by a notification sender who accepts feedback instead of hiding behind a no-reply address. Lacking real message authentication and authorization tools, we have to look at a mixture of content and metadata patterns to try to sort it out. In this every gray world, I can imagine reciprocity being a useful measure...