[epicureanideal]

There are still solutions in that case. Email addresses only allocated to verified humans, which only accept email from the same addresses or specifically allowed outside email addresses.

Alternatively, email addresses that are necessarily paid for that have maximum sending limits or extra costs above those limits, so those addresses are not profitable for spam bots to use.

I could imagine some kind of “super priority email” that costs a dollar or something, that gets prioritized and is very unlikely to be marked spam.

More ideas: Maybe the amount paid per email sent changes depending on the percent of previous emails marked “accept emails from this sender”. Maybe some percentage of the e-mail fee is given to the recipient of the email.

Note that if a highly spam resistant email account is adopted by everyone the amount of spam sent may fall significantly. Gmail doesn’t count because it still isn’t as good as a system where sending millions of spam emails is simply too expensive.