I wouldn't do a mailing list these days, but as someone who spent the early part of my career interacting with devs that preferred this method, it's actually pretty ergonomic by a 2005 standard. A message thread aware, text based email client that can turn messages into patches in a keystroke makes it actually pretty comparable to modern code review...
I think it's hard for younger devs to get this because they're used to email being stuck in a crappy, unthreaded browser interface or Outlook etc. (which are terrible for mailing lists) and most collaboration taking place in code review and chat platforms like Teams/Slack but for decades before these were feasible, email was the way...
I'll note that a number of groups and forums send mailing list like emails (google groups, django dev being a big one) and that notifications can be threaded from places like Github with the right client.
Thunderbird has good threading.
Roundcube webmail is also capable here. Though when I have had it working it didn't include sent messages... which is not great in my mind.
That's most definitely the wrong tool (discord is not for async) and the other end of the spectrum. Or did you maybe misunderstand him saying "discourse"? That would make much more sense as a mailing list replacement.
@onlinepersona I will admit that the search feature in GNU Mailman could use an upgrade on its archive search.
I actually get all of my mail list posts right here in Friendica as I use kill-the-newsletter to subscribe and "friend" the RSS so post just show in my social media feed the same as Mastodon Toots and Lemmy Posts, so they don't overcrowd my email inbox.