If you already know you have access for the mailbox, setup for the account follow below description.
Open Outlook:

  • in the top Menu click Outlook and Preferences.
  • Accounts
  • Advanced
  • Delegates
  • Below the box: People I am delegate for:
  • Click on +
  • Write in the name on the mailbox.
  • Mark the name and click ok.
  • Ok
  • Close down any Settings window you have open.
  • The mailbox appears in left window of your screen. Click on the ARROW to open it up. After a few minutes it will have synchronised.