postfix gmail로 메일 릴레이 설정
참고한 웹페이지들 : https://rtcamp.com/tutorials/linux/ubuntu-postfix-gmail-smtp/ http://machoda.tistory.com/entry/xe%EC%97%90%EC%84%9C%EB%A9%94%EC%9D%BC%EB%B3%B4%EB%82%B4%EA%B8%B0-%EC%9C%84%ED%95%B4-%EB%A9%94%EC%9D%BC%EC%84%9C%EB%B2%84-%EA%B5%AC%EC%B6%95%EC%82%BD%EC%A7%88 http://blog.jicoman.info/2013/08/postfix_install/ http://d.hatena.ne.jp/ayokoyama/20061207/p1