Does it work though? Nobody runs such systems at scale, for very good reasons, because maildir just sucks in so many ways. Horses have also been battle-tested,

Does it work though? Nobody runs such systems at scale, for very good reasons, because maildir just sucks in so many ways. Horses have also been battle-tested, they're well-understood, but they don't transport tonnes of cargo and getting kicked in your face because they don't like you isn't pleasant. So if it takes a custom schema in a (No)SQL database, so be it, it's simply so much more performant, scalable, reliable and usable. It's simply idiotic how much maildir-based software starts "dying" at around 100000 emails in a folder, in 2023!