Subscribe to public and shared mailboxes in Mail on Mac
In the Mail app on your Mac, view account information for the IMAP account that provides shared and public mailboxes.
In the Account Info window, click Subscription List.
In the list of available mailboxes, select the ones you want to subscribe to, then click Subscribe.
To unsubscribe from one or more mailboxes, select the mailboxes in the Account Info window (or in the Mail sidebar), then click Unsubscribe.