Not disagreeing with your overall point, but: > - mailing lists software exist but they are another hack. There is no standard for subscribing or unsubscribing

Not disagreeing with your overall point, but: > - mailing lists software exist but they are another hack. There is no standard for subscribing or unsubscribing There is a standard for unsubscribing: https://tools.ietf.org/html/rfc8058 https://tools.ietf.org/html/rfc8058 And for subscribing, you can often open a mailto: link.