Re: still have a backdoor though right?
The IMAP protocol requires that emails which don't use S/MIME (that's 99.99%) are sent to the receiver in unencrypted form. They can be transmitted in transit by using SSL, but Apple would have to create the unencrypted email before sending it through SSL.
If the emails were stored in encrypted form, then Apple would still have to be able to decrypt those emails, so in practice storing them in encrypted form doesn't give any gain in privacy and no protection. Encryption can only help you if Apple cannot decrypt it, and with IMAP this just isn't possible.