Login to http://mail.yourdomain.com
On Main Menu under Administration, click ‘Alias Administration’
In Alias Administration Menu, Click the Add Alias button.
In the Alias text box, enter a name called “nobody” for the alias.
In the Destination text box, enter A Standard Alias (in this case admin), so that all mail sent to Yourdomain.com will forward to Admin@Yourdomain.com.
After entering the alias properties, click OK to add the alias. The new alias is added to the list of registered aliases.
The use of nobody alias also prevents messages from bouncing back
incorrectly-addressed mail to sender.