Open Outlook
Go to File
Select Account Settings
Click Account Settings again
Select your email account
Click Change
Click More Settings
Open the Advanced tab
Under Mailboxes, click Add
Type the shared mailbox name
Click OK
Click Apply
Click OK
Click Next
Click Finish
Restart Outlook
If needed, open the shared mailbox manually by going to File
Select Open & Export
Click Other User’s Folder
Enter the shared mailbox name
Click OK