A catch-all email mailbox receives emails sent to non-existent addresses under the same domain. For example, an email sent to the mistyped firstname.lastname@example.org will go to email@example.com in case the catch-all feature has been enabled for the latter. Thus, you can get email messages from acquaintances or customers 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 disabled. Just one single mailbox per domain name can be a catch-all one and email forwarding cannot be enabled 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 redirected to a 3rd-party mailbox.