The one caveat with Ghost is that it only works with Mailgun for drop-in support of sending newsletters: https://ghost.org/docs/faq/mailgun-newsletters/

It was the one thing that gave me pause before taking the leap. At least they're being transparent about what and why even if I disagree with some of their reasoning. I have sent newsletters successfully via a self-hosted SMTP server to thousands of readers for years. I mean, I wouldn't recommend anyone doing that if they value their sanity, but I also think self-hosters should be free to experiment.