A catch-all email mailbox receives email messages sent to invalid addresses under the very same domain. For example, a message sent to the miswritten email@example.com will go to firstname.lastname@example.org in case the catch-all feature has been activated for the latter. Thus, you can get messages from partners or customers 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. Just one mailbox per domain can be a catch-all one and email forwarding cannot be set up for such a mailbox. The latter is due to the fact that at some point you may start receiving spam messages in the catch-all mailbox and the forwarding restriction means that the spam will not be re-sent to a 3rd-party mailbox.