You can't address an email to a group in Mail in iOS either, though you can in OS X's Mail. You can't create groups in iOS's Contacts, but you can see those created in OS X's Mail. There are several such gaps in the fabric that persist even today that Apple needs to remedy. Still, Apple has set the bar for a highly integrated fabric, so when it fails, it's Apple fault. In that regard, Apple's unification state is much better than its competitors'.
Google's services - Maps, search, Gmail, Calendar, Drive, Now, and so on - are similar across platforms but not expected to be the same, perhaps because Google doesn't face compatibility issues with a desktop version of Android or a mobile version of Chrome OS.
Sure, there's a huge gap between how Microsoft services and apps work across Windows 8, Windows RT, and Windows Phone. They see the Apple promise of a common computing fabric and get upset when they encounter a tear or hole in that fabric. Apple users experience the frustration precisely because the common apps and OS-level functions are almost the same. Persistent inconsistencies among the "same" apps between OS X and iOS - and sometimes across different types of iOS devices - are an ongoing frustration with users. | Subscribe to InfoWorld's Consumerization of IT newsletter today. [ All about iOS 7: How Apple's new iOS 7 management APIs change the game for business.
They work increasingly the same across Apple's full range of devices - except when they don't. It's even more evident in Apple's applications: Mail, Calendar, Contacts, Reminders, Notes, Messages, Safari, Maps, iTunes (if you include iOS's Music, Videos, iTunes U, and Podcasts apps as part of the iTunes family), iBooks, iMovie, iPhoto, GarageBand, Pages, Numbers, and Keynote. You see that with the adoption of iOS-style gestures and text-entry shortcuts in OS X, as well as in iOS 7's adoption of the App Exposé-like view of running apps.
External recipients will not see the Sent on behalf of address in the From field – they will see the actual sender's email address.
NB - If you can't see the address in the GAL you may need to manually update your offline address list.
If a mailbox doesn't exist in Exchange Online, – e.g.Members of shared mailboxes are given 'Send as' permissions and can then send mail as the primary email address of that mailbox.