> While the Postgres community has an older and sometimes daunting contribution process of submitting patches to a mailing list, [...]

The Linux kernel works the same way.

What are other big open source projects using if they are not using mailing lists?

I could imagine some using GitHub but IME it's way less efficient than mailing list. (If I were a regular contributor to a big project using GitHub, me being me, I would probably look for or write myself a GitHub to e-mail gateway).

You can already subscribe to projects or single issues/PRs on github and reply via email to post comments.

I can understand not wanting to use GitHub/GitLab/etc. for various reasons. But I don't understand how usability vs mailing lists is one.

How is a set of 9+ mailing lists any better? It has significantly worse discovery and search tools unless you download all the archives. So you're creating a hurdle for people there already.

Then you have people use all kinds of custom formatting in their email clients, so consistent readability is out the window.

People will keep top-posting (TOFU), transforming the inconsistent styles in the process. Creating an unnecessarily complicated problem for your email client to "detect quotes", or you have to keep reminding people.

Enforcing structure of any kind in email lists seems so tedious. I'm not advocating for bugzilla style "file out these 20 nonsensical fields before you can report anything" but some minimal structure enforced by some tooling as opposed to manual moderation seems very helpful to me.

Kubernetes works through GitHub and that's probably one of the bigger ones.