I never appreciated that this could be used for "email". I can see how the simple user address feature plays right into this nicely too.
In addition to spam emails, something like this could be a used as an impetus to help reduce "cc" or "reply to all" emails - often just a case of laziness.
Email being free is actually costing us all in time and therefore money. Micropayments like this (with a tiered system for those that opt for it as you propose) could provide a solution.
Many thanks for sharing this - huge food for thought.
Totally agree, thanks for reading!