A catch-all mailbox receives emails sent to non-existent addresses under the very same domain name. For example, a message sent to the mistyped firstname.lastname@example.org will go to email@example.com in case the catch-all feature has been enabled for the latter. In this way, you can receive messages from mates or customers who may have sent a message to your email address with a typographical error or to an outdated one, which they may still have, but you have already deactivated. Only one single 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 begin receiving spam emails in the catch-all mailbox and the forwarding restriction means that the spam will not be redirected to a 3rd-party mailbox.