If you aren’t seeing a shared mailbox in your Outlook client after 24-48 hours of its creation, you may have a corrupted OST file. Use these steps to configure Outlook to not cache shared mailboxes:
In the Outlook client, click the File tab in the upper-left.
Select Account Settings, then select Account Settings again inside that menu.
In the Account Settings dialog, click Change from the menu on the Email tab.
Click the More Settings box.
Select the Advanced tab.
Unselect the checkbox for Download shared folders.
Click Apply and restart Outlook.