A catch-all mailbox is one that captures all the messages sent to invalid addresses. For instance, if your address is firstname.lastname@example.org, but somebody miswrites it and sends an email message to email@example.com, it will still be received in the catch-all mailbox that you have configured. Just one mailbox per domain can have this feature enabled and in this way you will never miss messages because the other side has an obsolete email address or has made a spelling mistake. The disadvantage of creating a catch-all mailbox is that you may begin receiving plenty of spam emails, but this issue can be fixed using an anti-spam protection solution. It is also essential to bear in mind that a mailbox with an activated catch-all feature cannot forward inbound emails to a 3rd-party address.