The default e-mail address will "catch" any mail that is sent to
an invalid e-mail address for your domain. All mail that is sent to an address
that does not exist will go to the default e-mail address. To send all default
mail to the main mail account, simply type the user name of your cPanel account
in the e-mail address input field.
This allows you to set the default e-mail address to discard any e-mail sent
to it (which is not recommended) or pipe the e-mail to program or application
that resides on the server.