When I just finished installing ISPConfig(1-2 minutes), my email was sent to Yahoo successfully in Mail Box. When the time pass for about 1 hours, my email that sent laster will be in Bulk in Yahoo. Do anyone has any idea. Any change that ISPConfig made? I use Mandriva, Postfix with default value when install, Co-location server without own DNS. My ISP use PRT Record in DNS, which they claim that it is ok. thanks all.