[massaman_yams]

> "... small non-spam senders would congregate" Congratulations, you've invented the email service provider. Most small non-spam senders don't want to spend the time figuring out IP reputation, DKIM, or SPF already, so they pay someone to do it for them. What makes netblock reputation different?

Reputation isn't public because then spammers game it and you get worse filtering outcomes. ISPs learned this the hard way.

[pas]

sure, there is no problem with having 95+ % or more handled by professional industrial companies

the problem is that they literally don't even allow others at the table, only way is to force yourself a seat by having enough traffic

[massaman_yams]

Is it getting harder to self-host? Yes. Impossible? No. Most senders just find it easier to pay for it.

[pas]

Everything is getting harder as tech gets more and more complex. (As IT matures.) That's okay. The problem is that the incentives suck and there's too much business in email. The big ones have built their moats, and there's not much to do.

"SMTP" was simply never made to be resistant to this. (Nor the web in general.)