Please always show all mailboxes on the left navigation panel (don't like the “more” and “less” feature that hides other important mailboxes).

Or, that would be nice if it becomes an relevant option of user's choice in the Settings.

It is because sometimes some legit emails would be put in the Spam mailbox. If the left navigation panel was by default hiding these mailboxes until user manually clicking the “more” thing to reveal the Spam mailbox, user might have not paid attention to those emails and missed something.