A catch-all mailbox receives messages sent to non-existent addresses under the exact same domain. For example, an email sent to the mistyped firstname.lastname@example.org will be delivered to email@example.com if the catch-all feature has been enabled for the latter. In this way, you can get emails from acquaintances or customers 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 deleted. Only one single mailbox per domain can be a catch-all one and email forwarding cannot be activated for such a mailbox. The latter is due to the fact that at some moment you may start receiving spam email messages in the catch-all mailbox and the forwarding limitation means that the spam will not be redirected to a 3rd-party mailbox.