A catch-all mailbox is one that collects all the emails sent to invalid addresses. For instance, if your email address is email@example.com, but someone miswrites it and sends a message to firstname.lastname@example.org, it will still be received in the catch-all mailbox that you have set up. Just one single mailbox per domain can have this feature enabled and thus you will never miss messages because the other party has an out-of-date email address or has made a typo. The negative aspect of having a catch-all mailbox is that you may start receiving a lot of unsolicited bulk messages, but this problem can be rectified by using anti-spam protection software. It is also crucial to remember that a mailbox with an active catch-all feature cannot forward inbound messages to a third-party address.