EmDash with some aggressive caching and SWR is effectively this, and we're getting closer to that every day. When the cost of maintaining the data part of the CMS is effectively free, you're basically working with a static site anyway.
I find it a little funny that their blog post goes into a lot of righteous detail on why they don't charge for address space like other providers and then on their pricing page they charge for you to receive or send emails.
Receive! Like the moment someone knows you are using them as a provider they would be able to DoS your account as no other provider charges this way.