Server :: Permanently Block Access To Email From Japan?

I run my own home server using OpenSuse 11.1, everything is setup using apache, php, etc etc, and it all works perfect, but now I need to use my own email server for the use of Dolphin social networking software, so that when someone registers, the email server sends out registration confirmation emails, so I set up postfix, yeah right!!!, even though I followed all instructions to set postfix as a closed relay, a test done at mxtoolbox site still said it was an open relay, but while I was trying to set up postfix, my access to the server slowed down, and my servers drive light was constantly active,,, so when I look at the mail queue, I saw 4000+ emails, all from japan, (hinen.net), so I promptly shut down postfix and use postsuper -d ALL in the command console to delete the queue, but no matter how I try, I couldn't configure postfix as a closed relay,,, so I uninstalled it and installed sendmail, and using webmin, I could use a spam list and block the domain, now, sendmail's test at mxtools show as a closed relay, I can't even send out a test email using smtp auth, but disabling auth, I can, but now my IP is blocked at spam cop, and spamhaus,,, gmail server say my IP is not authorized to send to their servers, but to use my ISP relay instead,,, but my ISP doesn't have a relay,,hence the need to run my own email server.

My home server uses double layer firewall, a hardware firewall between the internet and the server, and a software firewall on the server, and I only allow the ports I need, IE, 80 = http, 443 = https, 20/21 = ftp, 25 = smtp, 110 = pop3. and that's all, but any other internal access from my workstation to the server, using ssh, I only open the ports on the server firewall. If someone here has a great deal of knowledge on sendmail, and can set up a an M4 (linux.mc) config file for me, it would be much appreciated. What I would like my email server to do, is to only allow the sending of emails from inside it's own server system,, ie, when a php script sends an email to the server, then the email server would let it through, but anything else, outside the local network is ignored.