For what it’s worth, this has not been my experience after self hosting my email for nearly a decade. It has not been a constant battle at all… it has just worked, and I get responses whenever mailing random people all the time and have not had delivery issues to my knowledge. That said, I have talked to people who have had issues and every time there has been something wrong with their configuration (usually DKIM or rDNS is not set up properly). There’s enough that can go wrong that I wouldn’t recommend people send important emails with it unless they’ve been doing it for a while and they’re sure it’s working, but in my experience this is all fear mongering. Self hosting your email is very doable and is generally not a constant battle against getting put in the spam slammer. There’s a lot of picky little things to set up at first, but once it’s set up it’s usually fine.