If someone has shared a mailbox with you but it is not showing in Outlook, these are the steps you should take to bring it up.

  1. Click on File
  2. Go to Account Settings -> Account Settings
  3. In the pop-out window double-click on your email address:
  4. Click on "More Settings"
  5. Click on the "Advanced" Tab, ensure the "Download Shared Folders" checkbox is unchecked and click OK
  6. Close and reopen Outlook
You should now see your shared mailbox appear under your emails within Outlook