A catch-all functionality that is enabled for a specific mailbox will permit you to receive emails that are sent to email addresses that do not really exist. To put it differently, if you delete an email address and somebody still sends an email to it, or to any miswritten email address under the same domain name, you will receive the email in the catch-all mailbox. Using this feature means that you will no longer miss an email for any reason, which could be vital in case you run a business, for example. Since you may start receiving spam messages, you can combine the catch-all feature with anti-spam filters in order to get only legitimate messages 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.