A catch-all mailbox receives emails sent to non-existent email addresses under the very same domain name. For instance, a message sent to the misspelled email@example.com will go to firstname.lastname@example.org if the catch-all feature has been enabled for the latter. In this way, you can get messages from colleagues or clients 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 disabled. Just one single mailbox per domain can be a catch-all one and email forwarding cannot be enabled 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 limitation implies that the spam will not be redirected to a 3rd-party mailbox.