Worth mentioning, if you want a docker-compose ready email server/service there's mailu[1]. It's relatively easy to get up and running, and will guide you through the DNS records for secure mail. I've got a couple test domains up so far, and it's mostly been good. Some outlook.com (not o365) domains have been problematic though, I'm sure everyone has stories here.

If the article's solution were open-source, would be interested in seeing the UI/UX. I also looked into WildDuck with great interest but the lack of good UI/UX is mostly what held me back. If I didn't have to work for a living, and was less lazy, I might have written something.

    1. https://mailu.io/