A catch-all email mailbox receives messages sent to invalid email addresses under the very same domain name. For instance, a message sent to the mistyped firstname.lastname@example.org will be delivered to email@example.com if the catch-all feature has been enabled for the latter. In this way, you can get emails from partners or clients who may have sent a message to your email address with a typo or to an outdated one, which they may still have, but you have already deactivated. Just one single mailbox per domain can be a catch-all one and email forwarding cannot be set up for such a mailbox. The latter is due to the fact that at some moment you may begin receiving spam emails in the catch-all mailbox and the forwarding restriction implies that the spam will not be delivered to a 3rd-party mailbox.