This is a very convenient feature. A catch-all account can receive any e-mail that is not sent to an account at your domain name for which there is already an address set up. For instance, if one of your addresses is jim@yourdomain.com, and someone sends you an e-mail to jin@yourdomain.com, you will still receive the e-mail!!
To setup a catch-all address, simply create a normal alias address from the Customer Control Panel, using “anybody” as the local part, so:
anybody@your domain, and specify where you want it to go.
So, for example, if you create:
anybody@your domain -> help@mrhost.ca
Then any address, not previously setup, @ your domain, would automatically redirect to help@mrhost.ca