A catch-all email mailbox receives emails sent to invalid addresses under the very same domain. For example, a message sent to the mistyped firstname.lastname@example.org will be delivered to email@example.com in case the catch-all feature has been activated for the latter. Thus, you can receive messages from friends or clients who may have sent a message to your email address with a typographical error or to an old one, which they may still have, but you have already deleted. Only one single mailbox per domain name can be a catch-all one and email forwarding cannot be set up for such a mailbox. This is due to the fact that at a certain moment you may start receiving spam email messages in the catch-all mailbox and the forwarding restriction implies that the spam will not be sent to a third-party mailbox.