Do you run your email server? I run two, have next to no problems (the key is in setting up DNS correctly, as I mentioned) and keep getting told this by people who have never tried.
I made sure to include the word correctly in the reply. Mox mailserver tells you exactly what to do. I think mailcow does as well. A lot of people don't do it and then tell others that selfhosting email with good deliverability is impossible. You set it up once and you're good to go
