NOTE: The OWA App is no longer supported.

A longstanding hindrance in getting customers to agree to switch to using actual shared or resource mailboxes as opposed to User mailboxes (tied to guest accounts, which our ISO frowns upon) posing as role-based mailboxes or rooms has been their need to access such mailboxes via mobile devices.  This stems from the limitation of ActiveSync not permitting access to multiple mailboxes in an Exchange service via a single set of credentials.

I’ve now found a workaround for this limitation using the OWA App for iPhone, iPad, and Android.  There is a trick to accomplishing this, and it is not well documented, but after much fiddling, I’ve managed to figure it out.

The secret is to start in OWA.  Not the app, but browser-based OWA.  The following steps have to be done in OWA. It will not work to do this in the Outlook desktop app. Suppose I have permissions to access the Inbox and Calendar folders of a room resource mailbox.  Here are the steps to expose those folders to me in the OWA App.

1. Start off by logging into OWA.
2. In the left-hand navigation bar under “Folders”, click “More” to expose the full folder list.
3. Below the Favorites list, there should be a line with your mailbox name. Right-click that and select “Add shared folder…”
4. In the “Add shared folder” dialog, search the directory for the desired mailbox and click “Add”.
5. Now, from the “waffle” app launcher icon, select “Calendar”
6. In the left-hand navigation bar, right-click “My Calendars” and select “Open calendar”.
7. Once again, find the target mailbox and click “Open”.

Now that everything is staged in OWA to expose the shared mailbox, we can move on to configuring the mobile OWA App.  Please note that, if you’ve already configured your account in the OWA App, the shared folders won’t auto-populate in the folder list in the app.  We actually have to reset the app and configure it from scratch to force a refresh of the listing. To do so, perform the following steps. (These are the steps for doing so on iOS.  Android users will need to figure out the corresponding steps on their own since I don’t have an Android device with which to test.)

1. On the iOS device, close the OWA app if it is already open. (Double-press the main button, scroll left or right to find the running app, and swipe up to kill it.)
2. Open the Settings app and scroll down through the listing of apps to find the entry for OWA, then select it.
3. Turn the “Reset Application” setting ON.
4. Now, go back to the main screen and turn on the OWA app.
5. Tap on “Continue” on the “Before you start” screen.
6. Enter your email address and tap “Sign in”.
7. You’ll then be prompted to enter your password.  Do so and tap “Sign in” again.
8. Now, once you are fully logged into your mailbox, tap the three-bar “hamburger” icon in the upper left-hand corner.
9. This will expose the list of available mailboxes and folders.
10. Expand the mailbox you added earlier in OWA to show its list of folders, then tap the folder you wish to view. Lo and behold, the selected folder will then be displayed.
11. To see the calendar of the mailbox you’ve added, click the calendar icon at the bottom of the screen.
12. Click the previously-mentioned control icon in the upper left-hand corner to expose the calendar list.
13. Tap the calendar you wish to view.  (You may wish to de-select your own default calendar at the top of the list.  Otherwise, the resulting view will present a superposition of both calendars.)
14. Tap the previously used control to bring the calendar view back in place.

And there you have it.  Viewing shared or resource mailbox items (or even shared items from another user mailbox) in the OWA App for mobile devices.