Get every email addressed to your domain, even if the mailname doesn't exist.

With the catch-all facility you can redirect all mail addressed to your domain to a specified email address. So unless there is a specific mailname defined already an email message will can be redirect to another address. This facility is useful when your friends/customers misspell your email address... usually when this happens the email will not be delivered because it is not a valid address, with the catch-all in place you can be sure you will receive it.