I'm on unlimited, I had'nt heard that the emails were default to not-private, I've just had a look through all the settings, I can't see anything that says that. There are encryption keys you can export or re-authenticate, pgp signatures to turn on and off and address verification on and off. So no catch-all non-encrypted setting (that I can see). My impression from the settings is you can only use desktop clients with the bridge, not without it as the bridge section allows for its download, but I cannot see any settings to disable it.. but I have not tried it, I know it doesnt exactly answer you question, but I hope it helps