Hey testing creating blog posts from a simple email Posted by beverett on Wednesday February 24, 2021 @10:59AM from the world.hey.com dept. https://world.hey.com/jason/hey-world-b02a6f2e ( 2 comments | 3 points | on HN )
Looks like maybe it's been depreciated in the self-hosted version: https://codex.wordpress.org/Post_to_your_blog_using_email