How do I direct catch-all email into a mailbox?
The catch-all address is a forwarding address, and you can't directly make it be a mailbox. However, you can still direct mail sent to any address @example.com into a mailbox. To do so, just change the destination of the catch-all address to forward all mail to the mailbox in question.
For example, if you normally read email using a mailbox at email@example.com, change the catch-all address to forward any unknown mail to firstname.lastname@example.org. You can then read the incoming catch-all mail just like other mail sent to email@example.com.