(If you have granted the appropriate permissions to their mailbox)
1. Log in mailbox using Outlook Web App.
2. Right-Click your name in the folder list, Click Add shared folder from the drop down list.
3. Type the name of the mailbox you have the right to access in the Add shared folder and click OK.
4. The mailbox appears in your Outlook Web App folder list.
1. Right-click the folder and click Remove shared folder