An author posting original content is always a single point of failure. That's a problem based in the physical world and has nothing to do with the computer-based system by which they distribute their content.
If revx email host gets shutdown, he can find a new one easy peasy. revx can just update his domain's DNS records to point them to a new server.
The federated nature of email prevents any individual email host from being a single point of failure, which I would believe is the point when comparing publishing via email to publishing content via a social network platform.
I imagine that the mailing list is Bcc:, with themself as the To:. This would allow for such a setup. Of course this isn't "socially decentralised" but I doubt that's what most people are referring to when they talk about decentralisation.
This makes it sound like revx is the single point of failure.
The whole thing reads to me like the locus of centralisation lies entirely with revx.
I get that email is decentralised / federated.