There are outlier Mail-wonks who maintain pay-to-send wouldn't "work" but they are somewhat in a minority: If you forced senders to pay even tokenistic per-mail sums, the attractiveness of mail would disappear.
People don't want to monetize Mail for complex reasons. The "won't work" aspect in spam pushback has always been debatable.
(there's a well known checkbox list of "your proposed anti-spam mechanism won't work because.. which is a huge antipattern to having a rational debate about it)
The problems are regulatory: who sets the price, who collects the price, whats done with the money, and what it does to the ecology of email internationally. But, it would within some definitions of the term "work"