A catch-all mailbox receives emails sent to nonexistent email addresses under the very same domain name. For example, an email sent to the miswritten email@example.com will be delivered to firstname.lastname@example.org in case the catch-all feature has been enabled for the latter. In this way, you can get messages from friends or customers who may have sent a message to your email address with a spelling error or to an outdated one, which they may still have, but you have already disabled.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 set up for such a mailbox. This is so because of the fact that at a certain moment you may begin receiving spam messages in the catch-all mailbox and the forwarding restriction implies that the spam will not be sent to a 3rd-party mailbox.