A catch-all mailbox receives emails sent to inactive addresses under the same domain. For instance, an email sent to the mistyped firstname.lastname@example.org will go to email@example.com in case the catch-all feature has been activated for the latter. In this way, you can get messages from buddies or customers who may have sent a message to your email address with a spelling mistake or to an old one, which they may still have, but you have already deleted. Only one 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 begin receiving spam messages in the catch-all mailbox and the forwarding limitation implies that the spam will not be re-sent to a third-party mailbox.