Any email that is sent to an unknown account at your domain name, such as unknown@yourdomain.com, gets automatically rerouted to your default email account. All web site accounts are automatically assigned a default email address - user@yourdomain.com - which you can change, if required.
To set your default email address:
Click on the Default address link in the Mail Menu area.
Enter the complete email address of the new default in the Modify default address field.
Click on the Submit button. Your new default email address has now been set.