A catch-all mailbox receives email messages sent to inactive email addresses under the exact same domain. For example, an email sent to the miswritten suport@domain.com will go to support@domain.com in case the catch-all feature has been enabled for the latter. In this way, you can get emails from acquaintances or customers who may have sent a message to your email address with a spelling error or to an out-of-date one, which they may still have, but you have already disabled. Just one mailbox per domain name can be a catch-all one and email forwarding cannot be activated 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 limitation implies that the spam will not be re-sent to a 3rd-party mailbox.