It needs the ability to manage device access on a per device level and not a per mailbox level.
The OWA is a great tool and is a perfect alternative for the native mail client. However, there needs to be security work on this app. There should be the ability to allow or deny access to OWA on a device level not just mailbox level. This should be possible since I can see each OWA instant in the phone portion of a user's mailbox and this is broken out by device. This is a large issue for any corporation trying to manage email access to devices. Just turning off the ability for all devices is not the granularity that is needed.