Not true. We have plenty of clients using their own decentralized email servers and getting great inbox delivery of legitimate bulk email.

To get good results on your own server, you need:

(a) To be sending email that people want to receive.

(b) To have the technology setup correctly. It's not hard; we do it all the time for our clients.

(c) It's greatly beneficial to above ~20k messages/day on your own server. Not required, but being above that point lets the ISPs gather statistical data on your complaint and open rates, which allows reputation filters to click in.