Running a server is very doable. There are packages to deploy and configure almost everything for you and removing a ton of headache.
Getting your email recognized as not spam by the major providers is pretty much impossible. You need all sorts of stuff to help verify integrity including special DNS records and public identity keys, but even if you do everything right, your mail can very easily get black holed before it even reaches a user’s inbox because of stupid shit like someone abused your rented server’s IP years ago, and you can’t seem to get it off everyone’s lists.
Email as a decentralized tool has effectively been ruined by spam and anti-spam measures. You’re effectively forced to use a provider because it’s near impossible to make your outgoing mail work as an individual. I think some of those anti-spam measures are anticompetitive, but I do think some are just desperate attempts to reduce the massive flow of spam.