Ask HN: Could something like an email Tobin Tax work to reduce unwanted emails?

A Tobin tax was originally defined as a tax on all spot conversions of one currency into another. It was suggested by James Tobin, an economist who won the Nobel Memorial Prize in Economic Sciences.*

I think spam and aggressive email marketing is akin to currency speculation in some ways, but haven’t read about anything like a stamp or token for emails since Yahoo and AOL announced a plan in 2006 that never took off.*

Could it be done, to help reduce unwanted emails and raise and raise public funds for good causes like climate action? Anyone written about this or working on it?

* https://en.m.wikipedia.org/wiki/Tobin_tax * http://news.bbc.co.uk/2/hi/technology/4684942.stm