A catch-all mailbox receives emails sent to non-existent addresses under the same domain name. For example, an email sent to the mistyped email@example.com will be delivered to firstname.lastname@example.org if the catch-all feature has been activated for the latter. Thus, you can get emails from acquaintances or customers who may have sent a message to your email address with a spelling error or to an out-of-date one, which they may still have, but you have already deleted. Only one mailbox per domain can be a catch-all one and email forwarding cannot be set up for such a mailbox. This is so because of the fact that at some moment you may start receiving spam emails in the catch-all mailbox and the forwarding limitation implies that the spam will not be sent to a 3rd-party mailbox.