Email data is by default secured and encrypted on the iOS device. information cannot be leaked unless the device passcode is broken and if the device is compliant.(meaning it would have to have checked in to the server with in a specified period of time) if that is not the case or if the phone hasn't already been remotely wiped then the data will not be able to be accessed or leaked. There is currently no container available for iOS but there is encryption for the corporate data native to the iOS device that EMM already enforces and takes full advantage of. That is the very reason there is no secure container for iOS yet, because Native encryption and security features were already available from Apple. android on the other hand did not offer any options for encrypting the corporate data so the container was released for Andorid to offer the same kind of security that the device/Os did not have.
There are discussing of introducing an apple container but nothing concrete. if you want, you can submit a Product Enhancement request for this feature.