@jdaviescoates thank you - I've got mail restored using backup, which required a few hours, but the data is there.
But I can't really can't see any reason keeping it enabled by default. How many modern mail clients can't handle search across all folders?
I understand that you can't satisfy everyone with changes - just wanted to let you know that I'm on the side that is shall not be a default; unless I'm missing something, people lived happily up till 7.5.1 🙂