These days almost every mail server will send mail over tls, but it’s not a guarantee which is a little unfortunate. Like you say there’s always privacy concerns with email, unfortunately.

I think in terms of privacy it really depends what you care about and what you’re using it for. If you care about Google reading your inbox, then self hosting can in theory help (at least for emails where the other party isn’t on Google or whatever)… Personally I like the idea of Google not knowing every company that I have an account with and everything I order online, which is information that’s definitely in your inbox. If you care about obscuring who you are to services that you sign up for with email, then arguably self hosting is not ideal because you’ll be the only one using that domain for email, and you might be better obscuring yourself through something like Apple’s “hide my email” service (which of course means you trust Apple to see those emails instead).

If you have more serious concerns and are having conversations that you don’t want anybody other than the recipient to know about email is probably the wrong choice for that conversation, but PGP is a decent option in these cases, albeit too clunky for most people. You may consider other services like protonmail or tutanota, but there are concerns with these services as well (eg, protonmail gets some flack for not encrypting metadata like message subjects, which is a big deal) and again there aren’t necessarily good guarantees for anybody you’re talking to on gmail or whatever.

Personally I like self hosting my email because of the flexibility that it offers and the price. It’s nice to be able to have as many email accounts as I want and it’s cheap to host, and I enjoyed learning about it and setting it up. My personal inbox is out of the hands of giants, but obviously if I’m emailing normal people it’s probably going to be available in the clear to Google or Microsoft (which is likely the case regardless of your solution). That’s not ideal, but it’s the reality right now with email. I kind of think of email more like a Twitter account or something at this point. It’s a semi-public way for random people to get in touch with you and a lot of conversations might be kind of explicitly public like on mailing lists, or something more akin to talking to a colleague in a public space — not super private, but a convenience, I guess?

I’d still recommend that people do try to self host their email if they’re thinking about this. Independent mail servers seem like a healthy thing for the web and learning more about it will give you a better sense of how secure / private your emails really are. Things like protonmail seem to have some advantages, but I also get some weird vibes from them and I’m not sure how much of a privacy increase they really give if you aren’t talking to other protonmail users and stuff anyway.