A catch-all mailbox receives emails sent to invalid email addresses under the same domain. For example, an email sent to the mistyped suport@domain.com will go to support@domain.com in case the catch-all feature has been activated for the latter. In this way, you can receive email messages from pals or customers who may have sent a message to your email address with a typographical error or to an obsolete one, which they may still have, but you have already disabled. Just one mailbox per domain can be a catch-all one and email forwarding cannot be enabled for such a mailbox. This is so because of the fact that at some moment you may start receiving spam email messages in the catch-all mailbox and the forwarding restriction implies that the spam will not be re-sent to a 3rd-party mailbox.