Before adding a shared mailbox to Outlook, you must ensure with the mailbox owner that you have been given privileges to do so. Once you have confirmed your access, follow the instructions below to add the mailbox to Outlook.
Windows 10 Users
1. Open Outlook.
2. Select the File menu.
3. Select Account Settings.
4. Select Account Settings again from the drop down menu.
5. Select your email address from the list, and then select Change.
6. Select More Settings.
7. Select the Advanced tab.
8. Select Add.
9. Enter the email address associated with the shared mailbox, and then select OK.
10. Select OK.
11. Select Next.
12. Select Done.
macOS Users
1. Open Outlook.
2. Select File > Open. 
3. Select Open.
4. Search for the email address for the shared mailbox and click Add.
Office 365 Online
1. Open Outlook.
2. Select your account icon in top right corner of the page.
3. Select Open another mailbox.
4. Enter the email address for the shared mailbox and select Open.
