A catch-all email mailbox is one that collects all the messages sent to invalid email addresses. For example, if your address is email@example.com, but someone mistypes it and sends an email to firstname.lastname@example.org, it will still be received in the catch-all mailbox that you have configured. Only one single mailbox per domain can have this feature activated and in this way you will never miss emails because the other party has an out-of-date email address or has made a spelling mistake. The negative aspect of having a catch-all mailbox is that you may begin receiving plenty of spam emails, but this issue can be solved using anti-spam filtering software. It is also essential to remember that a mailbox with an enabled catch-all functionality cannot forward inbound messages to a third-party mailbox.