A Catch-All system is where the mail server recognizes any address in your domain as a valid forwarding address. Some hosts don’t like offering catch-all services since they claim it generates more SPAM since any non-set address will forward to a designated address. However, a catch-all address allows for the customer to create email forwarding on the fly. For example, if they came across store1.com, they can create store1@you.com. If you start getting SPAM going to store1@you.com, you would know the responsible party, and can deal with the relationship you have with them.