A catch-all email mailbox receives messages sent to nonexistent addresses under the exact same domain. For example, an email message sent to the miswritten 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 receive messages from partners or clients who may have sent a message to your email address with a typographical error or to an outdated one, which they may still have, but you have already deleted.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 enabled 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 limitation implies that the spam will not be sent to a 3rd-party mailbox.