A catch-all feature that is enabled for a certain email mailbox will allow you to receive emails that are sent to addresses that do not actually exist. Otherwise stated, if you deactivate an email address and somebody still sends an email to it, or to any misspelled address under the exact same domain, you will get the message in the catch-all mailbox. Using this feature means that you will no longer miss an email for any reason whatsoever, which could be essential in case you are running a company, for example. Since you may start receiving junk messages, you can use the catch-all functionality with anti-spam filters so as to receive only real emails in your inbox. Just one single mailbox per domain can be a catch-all one and email forwarding cannot be activated for a catch-all mailbox.