I just finished migrating my Mailcow installation from a native Kubernetes port that I had made by hand and that was becoming impossible to update to a more streamlined (albeit wasteful with resources) deployment where I wrap docker-compose and a dedicated Docker instance in a Kata container that I run as a Kubernetes pod.
The container is built as a Nix expression and is available in my public Kubeia repository, which contains part of my Kubernetes deployment configuration and image build scripts. A README is available too, in case you would like to try running it yourself.
Do note that the Kubernetes deployment file is just provided as an example. It contains some pretty specific references to my particular deployment – view it as something like a template that you will have to copy and fill with your own data. Another idiosyncracy is that I really really dislike running multiple database servers on a single piece of hardware and so I kluged something in that makes Mailcow use my already provisioned MariaDB instance rather than its own. In other words, your mileage may very much vary.