terry carmen nhdnrcnysupportcom gary c new wrote issue spammers making raw socket connections postfix server spoofing one mynetworks domains server deliver valid recipient mynetworks domain smtp auth configured working method spamming unchallenged due viewed valid mynetworks domain best way postfix challenge method spam configure routers firewall accept connections packets outside world claim inside network actually happening much bigger problem postfix terry fri 08 aug 2008 055924 0500 challenging local senderrecipient spam