A catch-all mailbox is one that collects all the email messages sent to invalid addresses. For instance, if your address is email@example.com, but somebody miswrites it and sends an email to firstname.lastname@example.org, it will still be received in the catch-all mailbox that you have configured. Just one single mailbox per domain can have this feature activated and in this way you will never miss messages because the other party has an out-of-date email address or has made a typo. The disadvantage of using a catch-all mailbox is that you may start receiving lots of unsolicited bulk messages, but this issue can be fixed by using an anti-spam protection solution. It is also vital to remember that a mailbox with an enabled catch-all functionality cannot redirect incoming messages to a third-party mailbox.