A catch-all email mailbox receives emails sent to inactive email addresses under the exact same domain. For instance, 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. Thus, you can get messages from pals or customers who may have sent a message to your email address with a typo or to an outdated one, which they may still have, but you have already disabled. Only one single mailbox per domain can be a catch-all one and email forwarding cannot be enabled for such a mailbox. This is due to the fact that at a certain point 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.