A catch-all mailbox receives messages sent to non-existent addresses under the exact same domain. For example, an email sent to the miswritten firstname.lastname@example.org will go to email@example.com in case the catch-all feature has been activated for the latter. Thus, you can receive emails from colleagues or clients who may have sent a message to your email address with a spelling error or to an outdated one, which they may still have, but you have already deactivated. Just one single mailbox per domain name can be a catch-all one and email forwarding cannot be activated for such a mailbox. This is due to the fact that at some moment you may start receiving spam messages in the catch-all mailbox and the forwarding limitation implies that the spam will not be sent to a 3rd-party mailbox.