A catch-all mailbox is one that collects all the messages sent to non-existent email addresses. For example, if your address is email@example.com, but someone misspells it and sends an email message 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 thus you’ll never miss emails because the other side has an obsolete address or has made a mistake. The downside of setting up a catch-all mailbox is that you may start receiving a lot of spam emails, but this issue can be solved by using an anti-spam protection solution. It’s also vital to remember that a mailbox with an activated catch-all feature cannot forward inbound email messages to a 3rd-party mailbox.