How do I direct catch-all email into a mailbox?

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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 address@example.com, change the catch-all address to forward any unknown mail to address@example.com. You can then read the incoming catch-all mail just like other mail sent to address@example.com.