A catch-all mailbox receives emails sent to non-existent addresses under the same domain name. For example, an email sent to the mistyped firstname.lastname@example.org will be delivered to email@example.com if the catch-all feature has been activated for the latter. Thus, you can get email messages from colleagues or clients who may have sent a message to your email address with a spelling mistake or to an obsolete one, which they may still have, but you have already disabled. Only 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 moment you may start receiving spam email messages in the catch-all mailbox and the forwarding limitation implies that the spam will not be received in a 3rd-party mailbox.