A catch-all email mailbox receives messages sent to nonexistent email addresses under the exact same domain name. For instance, an email sent to the miswritten email@example.com will be delivered to firstname.lastname@example.org in case the catch-all feature has been enabled for the latter. Thus, you can get email messages from mates or clients who may have sent a message to your email address with a typo 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 enabled for such a mailbox. This is so because of the fact that at a certain moment you may start receiving spam email messages in the catch-all mailbox and the forwarding restriction means that the spam will not be redirected to a third-party mailbox.