I have been self-hosting email for 7 years successfully. But it required a physical server in a reputable datacenter, setting up Dovecot, Exim, SpamAssasin, reverse-DNS, SPF, DKIM. It took a bit of time to gain IP reputation but then it has worked flawlessly since. Occasionally some legit mail is flagged as spam or vice versa but it is not worse than any other mail provider. So it can be done! But my first attempts to do that on a VPS failed as IP blocks of VPS providers are often hopelessly blacklisted in major email providers.