참고사이트 :
http://phosphoros.tistory.com/1003
http://qmail.kldp.net/phpbb/viewtopic.php?t=7883
http://bmyluv.tistory.com/55
http://www.kokonu.info/index.php?db=so&id=43970
http://helpwork.wordpress.com/2011/10/10/gmail-smtp%EB%A5%BC-sendmail-%EB%A6%B4%EB%A0%88%EC%9D%B4%EB%A1%9C-%EC%84%A4%EC%A0%95%ED%95%98%EA%B8%B0/
네이버, 다음 SMTP/POP3 활용 :
http://www.lovelgw.com/Blog/187
유동 IP 에서 gmail 계정을 이용하여 Sendmail 설정하기