I second https://www.brainpickings.org/ and also would like to add http://nextdraft.com/ (though it is more "general news") - other than that I can't help, because I actually prefer to use rss-feeds over Newsletters.
(PS: You can also get rss-updates about new entries in Youtube-Playlists (google it) and if you use Twitter and follow some interesting people, that might also be a good way to stay up to date)