A catch-all mailbox receives emails sent to non-existent addresses under the same domain. For instance, an email sent to the misspelled firstname.lastname@example.org will be delivered to email@example.com in case the catch-all feature has been enabled for the latter. Thus, you can get messages from friends or clients who may have sent a message to your email address with a spelling error or to an out-of-date one, which they may still have, but you have already deleted. Just one single mailbox per domain name can be a catch-all one and email forwarding cannot be activated for such a mailbox. This is due to the fact that at a certain moment you may begin receiving spam messages in the catch-all mailbox and the forwarding restriction implies that the spam will not be sent to a 3rd-party mailbox.