Comment by oskapt

That is most often caused by reputation issues around the IP where your mail server lives. If you host it at home or in any “residential” block of addresses, then most definitely. Same if hosted on a VPS or with a provider whose address space may have been burned by spammers spinning up machines and then redeploying them when they start getting blocked. As someone said further down below, you can still host at home and use Amazon SES as your verified outbound relay. I do that with the Axigen free email server, and I have no issues with reputation.