A catch-all mailbox receives email messages sent to nonexistent email addresses under the exact same domain. For example, an email sent to the mistyped firstname.lastname@example.org will go to email@example.com if the catch-all feature has been activated for the latter. In this way, you can get emails from friends or clients who may have sent a message to your email address with a typo or to an out-of-date one, which they may still have, but you have already deleted.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 activated for such a mailbox. The latter is due to the fact that at a certain moment you may begin receiving spam emails in the catch-all mailbox and the forwarding limitation means that the spam will not be sent to a 3rd-party mailbox.