@molly0xfff Update - it looks like I can just go straight to Amazon SES. Since I'm already using that and have DMARC setup, I'm going to explore this.
So in the minutes since I've started reading your post, I've spun up an Ubuntu server at Vultr and will give it a go to try a self-hosted Ghost.
Will report back!
https://stackoverflow.com/questions/74680319/how-can-i-use-amazon-ses-with-ghost