When i try to follow your link instruction i can see the result ask below:
[root@vpserver log]# telnet mail.novpiseth.co.cc 25
Connected to mail.novpiseth.co.cc.
Escape character is '^]'.
220 vpserver.khmerwebhost.com ESMTP Postfix
250-AUTH PLAIN LOGIN
221 2.0.0 Bye
Connection closed by foreign host.
after that I have try to check /var/log/maillog
But i did not see anything.
Note: I was deleted maillog for let postfix to start new log for me easy to check the error. anyway since i deleted that file I could not see any log statement. Could you help this to me?