The default address will act as a 'catch-all', meaning it will catch all mail sent to an invalid address. 

To setup your catch-all follow these steps.

1. Log into your cPanel account. 
2. Navigate to the Email section and click "Default Address"

Email tab, cPanel

3. On the new page choose the domain name from the drop-down menu, check option Forward to email address and enter the email address to which emails are to be forwarded to

Default Address, cPanel

4. Click Change to save your changes

Thats it! Your catch-all address is ready to use.