In Outlook click FILE
Then click Info -> Account Settings… -> Account Settings…
Then click your account name on the list and click Change…
In the Change Account window, click More Settings… button.
Then, click Advanced tab-> Add… button-> in Add mailbox field type the name of the shared mailbox you want to add, f.ex: post.
Click OK in Add Mailbox window -> click OK in Microsoft Exchange window.
Click Next button in Change Account window.
Finally, click Finish button.
