***NOTE: This process is only compatible with the old version of Outlook***
1. With Outlook open:
1. Open the Tools menu
2. Select "Accounts"
2. Select the "Delegation and Sharing" button
3. Under "My Delegates", select the plus sign [+] button
4. Search for the mailbox you want to add and click on "Add"
5. Under the page below, select the properties and access you want the mailbox to have - then, select "OK"