Outlook - Viewing Other user's mailbox

You must use Microsoft Exchange Server as your mail service.

The shared folder must be stored in the Exchange Server mailbox.

The shared folder must have access permissions assigned.

Make sure that in Outlook you go to
Tools>Services
Click on exchange server, then properties
Click on the advanced tab.
Add the mail box there.
(if that is what you did before than there is something else wrong)
The other way that you may haveopened it(and i have done this too) if to go to file>open>other user's folder. By doing that you would have only see the inbox folder

To see the subfolders, the secretary needs to add the mailbox to the Exchange Server services in Tools | Services, on the Advanced tab. Then she'll see all the folders in the folders list.

Make sure she either has User permission on the entire mailbox or Reviewer permission on the top-level of the mailbox and any required folders.

Make sure that the secretary has access to the Inbox. To view subfolders, you must have access to the parent folder.

Regards,
Melody