A catch-all feature that is activated for a certain mailbox will allow you to receive emails that are sent to email addresses that do not really exist. Otherwise put, if you disable an email address and somebody still sends an email message to it, or to any misspelled address under the same domain name, you will get the message in the catch-all mailbox. Using this feature implies that you will no longer miss an email for any reason whatsoever, which could be crucial if you run a business, for example. Since you may start receiving junk emails, you can use the catch-all functionality with anti-spam filters in order to receive only real email messages in your inbox. Only one single mailbox per domain can be a catch-all one and email forwarding cannot be activated for a catch-all mailbox.