Sending email is already cheap, not free. Just so happens the cost is subsidized/hidden for most regular people and its so cheap that they give it away for free. For those of us that run transactional email, the cost is ~ $0.0001 per email for AWS SES, already at the fraction of a fraction of a cent you suggest.
Yes, but I want the rate to be variable depending on volume. I want it to be $0.0001 for a simple personal email. But if you send 10,000 emails today, I want it to cost you $100 (or more).
Many schemes to do this. Things like:
The first 10 emails is $0.0001 each.
The next 10 will be $0.001 each.
And so on. You can always fiddle with the thresholds and costs.
