A catch-all mailbox receives emails sent to non-existent addresses under the exact same domain name. For example, an email message sent to the miswritten firstname.lastname@example.org will go to email@example.com if the catch-all feature has been enabled for the latter. Thus, you can get email messages from mates 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 disabled. Only one single 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 email messages in the catch-all mailbox and the forwarding limitation implies that the spam will not be re-sent to a third-party mailbox.