A catch-all email mailbox receives email messages sent to non-existent email addresses under the exact same domain. For example, an email 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. Thus, you can get email messages from friends or clients who may have sent a message to your email address with a typographical error or to an old one, which they may still have, but you have already disabled. Just one mailbox per domain name can be a catch-all one and email forwarding cannot be activated for such a mailbox. This is so because of the fact that at a certain moment you may begin receiving spam emails in the catch-all mailbox and the forwarding restriction means that the spam will not be sent to a 3rd-party mailbox.