A catch-all mailbox receives messages sent to nonexistent email addresses under the same domain. For example, an email sent to the mistyped email@example.com will go to firstname.lastname@example.org in case the catch-all feature has been activated for the latter. Thus, you can receive emails from acquaintances or customers who may have sent a message to your email address with a typographical error or to an obsolete 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 activated for such a mailbox. The latter is due to the fact that at a certain moment you may start receiving spam messages in the catch-all mailbox and the forwarding limitation means that the spam will not be delivered to a third-party mailbox.