When adding users to a shared mailbox, it may take a few minutes before it populates on the user's end. Wait a bit and then close and restart Outlook again.


If that doesn't work, then manually add the shared mailbox to Outlook.



Launch Outlook.


Select the File tab on the ribbon, then select Account Settings > Account Settings.



Under the Email tab, ensure the correct account is highlighted, then choose Change.





Choose More Settings > Advanced > Add.


Type the shared email address.




Choose OK > OK.


Choose Next > Finish > Close.