A catch-all mailbox is one that captures all the emails sent to invalid email addresses. For instance, if your address is firstname.lastname@example.org, but somebody misspells it and sends a message to email@example.com, it will still be received in the catch-all mailbox that you have configured. Just one mailbox per domain name can have this feature enabled and in this way you will never miss emails because the other side has an obsolete address or has made a typo. The downside of setting up a catch-all mailbox is that you may start receiving lots of unsolicited bulk messages, but this issue can be rectified using an anti-spam filtering solution. It is also essential to know that a mailbox with an activated catch-all functionality cannot redirect inbound email messages to a 3rd-party email address.