A catch-all mailbox is one that captures all the emails sent to invalid email addresses. For instance, if your email address is firstname.lastname@example.org, but somebody mistypes it and sends a message to email@example.com, it will still be received in the catch-all mailbox that you have created. Just one mailbox per domain name can have this feature enabled and thus you’ll never miss messages because the other party has an outdated email address or has made a typo. The downside of having a catch-all mailbox is that you may start receiving lots of unsolicited emails, but this issue can be solved by using an anti-spam protection solution. It is also important to bear in mind that a mailbox with an active catch-all functionality cannot forward inbound emails to a 3rd-party mailbox.