A catch-all functionality that is enabled for a certain mailbox will permit you to receive emails that are sent to email addresses that do not really exist. In other words, if you disable an email address and somebody still sends an email message to it, or to any miswritten address under the exact same domain, you’ll 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 crucial if you run some company, for example. Since you may start receiving spam emails, you can use the catch-all functionality with email filters in order to receive only legitimate messages in your inbox. Just one mailbox per domain name can be a catch-all one and email forwarding cannot be enabled for a catch-all mailbox.