A catch-all functionality that is activated for a particular mailbox will permit you to receive emails that are sent to email addresses that do not actually exist. Otherwise said, if you remove an email address and someone still sends an email message to it, or to any misspelled email address under the exact same domain, you will receive the email in the catch-all mailbox. Using this functionality implies that you will no longer miss an email for any reason, which could be essential in case you run some company, for example. Since you may start receiving junk messages, you can combine the catch-all option with anti-spam filters so as to get only legitimate emails in your inbox. Just one mailbox per domain can be a catch-all one and email forwarding cannot be enabled for a catch-all mailbox.