A catch-all email mailbox receives emails sent to invalid email addresses under the same domain. For instance, an email sent to the miswritten suport@domain.com will go to support@domain.com if the catch-all feature has been enabled 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 old one, which they may still have, but you have already deactivated. Just one mailbox per domain name 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 a certain point you may begin 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.