A catch-all mailbox receives emails sent to invalid addresses under the exact same domain. For instance, a message sent to the misspelled firstname.lastname@example.org will be delivered to email@example.com in case the catch-all feature has been enabled for the latter. In this way, you can get emails from mates or customers who may have sent a message to your email address with a spelling error or to an obsolete one, which they may still have, but you have already deleted. Just one single mailbox per domain name 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 some moment you may start receiving spam email messages in the catch-all mailbox and the forwarding restriction implies that the spam will not be re-sent to a third-party mailbox.