I did not mean monopoly in the literal sense, just used it to express my feeling that a lot ends up flagged as spam that is not from these major corps servers.
Do you know how to read email headers? Are you subscribed to mailing lists? If yes, go to your inbox and check a few messages for the sender. You would be surprised at how many senders are there.
For transactional emails / regular mailing lists, I estimate that you just need like 0.25 FTE working on email, maybe even less. While this is not something everyone can do, there are tens of thousands email senders out there.