A catch-all email mailbox receives email messages sent to inactive addresses under the exact same domain. For example, an email sent to the misspelled 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 receive messages from pals or clients who may have sent a message to your email address with a typo or to an obsolete one, which they may still have, but you have already disabled. Just one mailbox per domain can be a catch-all one and email forwarding cannot be activated for such a mailbox. This is so because of 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 delivered to a third-party mailbox.