The default email address will "catch" any mail that is sent to an invalid email address for your domain. All mail that is sent to an address that does not exist will go to the default email address. To send all default mail to the main mail account, simply type the user name of your cPanel account in the email address input field.
Default Address Maintenance
Send all unrouted e-mail for:
Current Setting:Forward to email address
Forward to email address
Discard with error to sender (at SMTP time)
Failure Message (seen by sender):
Discard (Not Recommended)
Pipe to a Program:
/
When piping to a program, you should enter a path relative to your home directory. If the script requires an interpreter such as perl or php, you should omit the "/usr/bin/perl, or /usr/bin/php portion." Make sure that your script is executable and has the appropriate Hashbang at the top of the script. If you do not know how to add the Hashbang, just make sure to name your script file with the correct extension and you will be prompted to have the Hashbang added automatically.