A catch-all mailbox receives emails sent to nonexistent email addresses under the very same domain. For example, a message 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 receive emails from pals or clients who may have sent a message to your email address with a typo or to an obsolete one, which they may still have, but you have already disabled. Only one mailbox per domain can be a catch-all one and email forwarding cannot be set up for such a mailbox. The latter is due to the fact that at some point you may begin receiving spam email messages in the catch-all mailbox and the forwarding restriction implies that the spam will not be re-sent to a 3rd-party mailbox.