When the cost of spamming is near 0.00, all open platforms will be abused to the tilt. We have seen the email channel get less and less reliable with our own clients (password recovery, notifications and etc).
This might evolve into a couple of oligopolies (Microsoft 365 Outlook, Google Gmail, may be some legacy email providers like Yahoo) and if you want delivery you'd need to pay them, because they'd be the verifiers that you're not a spammer.
And these platforms will have a hell of time to fight the spammers that will create millions of email addresses and spam trough them.