A catch-all functionality that is activated for a specific mailbox will allow you to receive email messages that are sent to email addresses that do not actually exist. To state it differently, if you disable an email address and somebody still sends a message to it, or to any misspelled address under the very same domain, you will receive the message in the catch-all mailbox. Using this functionality implies that you will no longer miss an email for any reason whatsoever, which could be vital in case you run some business, for example. Since you may start receiving spam email messages, you can combine the catch-all functionality with anti-spam filters so as to get only real emails in your inbox. Only one single mailbox per domain can be a catch-all one and email forwarding cannot be enabled for a catch-all mailbox.