A beginner deliverability guide for open source geeks

A gentleman named Florian Effenberger, a long time "free and open source software enthusiast," has put together a neat little guide on email reputation and deliverability, aimed at folks who run their own mail servers and might know more about free and open source *nix-based mail systems, compared to the usual deliverability audience primarily made up of email marketers.

Here's links to part one (2021) and part two (2020) of "Return to sender – Florian’s beginner guide to improve e-mail deliverability." Definitely worth checking out!