[fencepost]

You beat me to it. Nine also allows easy connection to multiple Exchange accounts, has a variety of other nice features and has been around long enough to have a very solid track record.

This kind of sandboxing is one of the things third party apps like this have always been known for, going all the way back to a really old one whose name in blanking on which I believe maintained its own entirely internal calendar, files, etc. (Dataviz maybe?)

Edit: this may still be useful for some people, but the work profiles introduced in Android 5+ may make it less relevant at least for anyone at enterprise scale or otherwise using MDM through a service provider.