A catch-all mailbox receives emails sent to non-existent email addresses under the same domain. For example, 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messages from partners or customers who may have sent a message to your email address with a spelling error or to an outdated one, which they may still have, but you have already deleted. Only 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 point you may begin receiving spam email messages in the catch-all mailbox and the forwarding restriction implies that the spam will not be redirected to a third-party mailbox.