A catch-all mailbox receives emails sent to non-existent email addresses under the exact same domain. For example, an email message sent to the mistyped suport@domain.com will be delivered to support@domain.com if the catch-all feature has been activated for the latter. In this way, you can get messages from acquaintances or clients who may have sent a message to your email address with a spelling mistake or to an out-of-date one, which they may still have, but you have already disabled.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. The latter is due to the fact that at a certain moment you may begin receiving spam messages in the catch-all mailbox and the forwarding restriction implies that the spam will not be re-sent to a 3rd-party mailbox.