A catch-all email mailbox is one that captures all the emails sent to non-existent addresses. For example, if your email address is info@domain.com, but somebody misspells it and sends a message to inof@domain.com, it will still be received in the catch-all mailbox that you have configured. Only one single mailbox per domain name can have this feature enabled and thus you will never miss messages because the other side has an out-of-date email address or has made a typographical error. The downside of setting up a catch-all mailbox is that you may start receiving lots of spam email messages, but this issue can be rectified by using an anti-spam protection solution. It is also important to keep in mind that a mailbox with an enabled catch-all functionality cannot forward incoming emails to a 3rd-party email address.