A catch-all email mailbox receives emails sent to inactive email addresses under the very same domain. For example, an email message sent to the misspelled suport@domain.com will be delivered to support@domain.com in case 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 obsolete one, which they may still have, but you have already disabled. Only one mailbox per domain can be a catch-all one and email forwarding cannot be set up for such a mailbox. The latter is due to the fact that at a certain 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.