Over the course of a year the costs to send would be balanced by the profit from receiving for your average person but for spammers it would be untenable.
If you're trying to come up with a model that isn't using centralized companies to solve the problem for you then it's still a problem.
Part of the incentive towards centralization is because the spam problem is hard to solve in a decentralized way with the modern web.
I bet it's a lot. I bet there has to be a better way.
Is this a perception or do you have data on this?
See my response to parent. Email spam from the point of view of self-hosted infrastructure is no longer a problem in my experience. No megacorps needed (or wanted, IMO).
I set up SPF, DKIM, DMARC, used an IP not on any blacklists, and so on - everything guides told me I ought to do. Still, not only would my test messages often go to spam, I'm pretty sure I saw some vanish entirely, not even making it to the spam folder.
And this is a very insidious problem - did I e-mail X and they just didn't deign to reply? Or did my message never reach them?
I also wish there was a process for exporting/importing these lists.
With SPF/DKIM/DMARC (whichever of those verifies that the email header was actually set by someone who has access to that email sending address) on and open-relay on STMP turned off, I envision a web-of-trust-lite world (which is probably the wheel I'm reinventing) where I and everyone I exchange email-address-trust-cards like business cards help to crowdsource what is and is not spam based on shared whitelists and degree-of-separation weighting. If I think something is spam, my 1st degree of separation (who has handshaked with me to verify that yes we've met) also probably does, but his colleague, maybe not.
MUAs and online email service providers would check the compiled whitelist for each account before running their own spam filtering.
We have good online adblock lists, can we do the same for email spamlists without 27 clicks to whitelist or blacklist emails?
Servers would have to not blackhole spam-tripping emails and reply with 'you spam = bad', that is another problem entirely.
Spam in email is basically not a problem anymore, in my experience.
~15 years I would get literally thousands of spam emails per day in my spam folder. But this was the days when email servers were configured to accept anything no matter how malformed. And many people had misconfigured smtp clients, thus attempting to enforce constraints would drop a lot of legitimate mail. So spam was a huge problem.
Today it's very different. I no longer see any smtp clients from legitimate senders with any protocol misconfiguration. So for years now I enforce every detail at the smtp connection level (with postfix), before the email is accepted.
I still see failed attempts in the postfix logs but they get blocked right there. Actual spam getting through to the spam filter is down to a few a week.
Then checking DKIM drops all of these in the spam folder.
Spam that gets through these steps to my actual inbox is now so rare that it's always a surprise. Less than ten a year, tops.
So from my perspective (running my own email infrastructure for a handful of domains, personal and business, friends and family) email spam is no longer a concern.