I can confirm. I was self hosting my private domain and email for many years and lately I saw this behavior of big ISP and email providers that are trying to push private domains and in special those self hosted into spam lists. Even if you as admin you do all possible to clear out your email server/IP adding all necessary info DKIM / SPF / reverse DNS / PTR good MX config etc, they still kleep adding you in their paid spam lists.

I simply add to all my emails, if are sent to domains like outlook.com a simple note: stop using hosted email servers / providers to wake people up of this danger.

Slowly my personal contacts start using more personal domains and we have a nice and direct communication.

But yeah the threat is REAL and they push hard.