Shared mailboxes are not a new concept in Office 365 or in Exchange Server, although their use is not commonly known. Most Office 365 subscriptions even allow you to have shared mailboxes without paying additional license fees.
This walk though will show you how to add the shared mailbox to your outlook account if it does not automatically appear when you open outlook next. It is important that you give it time to propagate on the Office 365 / Exchange servers before you try to add it into your outlook.
Step 1. From the outlook main page (inbox) click file in the top left hand corner.
Step 2. Then click “Account Settings” and then account settings again.
Step 3. Double click on your account (should say firstname.lastname@example.org).
Step 4. Then click more settings.
Step 5. Click the advanced tab, then the add button.
Step 6. Just type the name of your shared mailbox and hit ok.
Step 7. Then click ok, next and finish and then down the bottom of your mailbox the new shared mailbox will appear.