Although you can add other users' mailbox folders to your Outlook Folder List without having any permission for their mailboxes, you will not be able to view them unless you have at least Reviewer permission.
The first step in opening another user's folder is to be granted permission.
a. Grant view access to the mail file
b. From the navigation pane, right click on the mail box email account name and go to "Folder Permissions."
Figure 1: Right click menu with "Folder Permissions" highlighted
c. Click "Add"
d. Find the user in the GAL to whom you wish to grant access
e. Under "other" check the box next to "Folder Visible"e. Click OK.Grant specific permissions to the individual folder in question.
f. From the navigation pane, right-click on the folder to be shared.
g. Go to "Properties."
h. Click the Permissions tab.
i. Click Add to enter the GAL and find the user who is to be given access and click OK.
j. Select the permission level in the drop-down and click OK.
Once permission has been granted, the individual folder can be added with the following steps:
a. From the File tab, select Account Settings. From the drop-down list, select Account Settings... . Highlight Microsoft Exchange, and click Change. Then, click More Settings... .
b. Click the Advanced tab, and then click Add... . This allows you to add mailboxes to your Outlook Folder List.
c. In the "Add Mailbox" field, enter the username or name (in lastname, firstname format) of the person to whose mailbox you have shared access.
d. You should now see the additional mailbox in the Folder List. Any folders that a user gives you permission to access should be listed under the other person's mailbox. If you cannot expand the Folder List, the other person has not given you permission to access the mailbox.