Funny headline, because every time I try to self-host anything important like mail, I learn how deep that field is and how little I know and that I'll probably need many many hours to do everything right and in a secure way (and my mails would still have a higher probability to be classified as spam). Then I think: "Screw it, I'll just use GMail"
Interestingly, it doesn't look like the author is self-hosting email. I know mail-in-a-box exists, but even with that I find it's worth the peace of mind to pay someone else for mail hosting.
I ran my own email server on my own domain for years. You're right, it's kind of its own special nightmare to integrate all the parts of a comprehensive email system (I eventually started using Zimbra's free server software because of it), but spam effectively killed being able to self-host more. Even if you setup SPF and DKIM and all the rest, you'll find yourself getting blackholed anyway because you're NOT Google or Apple or Microsoft. It's not like I even sent email in bulk either. It was just my normal, personal account. But getting OFF blackhole lists became enough work that I had to route my mail through Gmail anyway, so I just gave up self-hosting entirely. That was, like, 7 or 8 years ago, though, so maybe things are different now, but I doubt it. I expect it to only have gotten worse.