I've never tried to set it up even though I know it can easily be done with things like mailcow.

The downside is never really knowing if your email reached your recipient (maybe it got blocked by Gmail because of your IP, maybe some other reason). If I use Gmail/proton etc, then I can be pretty sure that the other person got my email.

Because it's not about setting it up, it's about not getting outgoing mail perceived as spam by someone. Borderline impossible without scale. Even doing everything correct is not enough.