: <<< 550 <x-ray at sehwamedical.co.kr>... Relaying denied : 550 5.1.1 <x-ray at sehwamedical.co.kr>... User unknown /etc/mail/relay-domains 에 sehwamedical.co.kr 을 입력하고 /etc/mail/access 파일에 sehwamedical.co.kr RELAY 를 입력한 다음 /etc/mail 디렉토리에서 makemap hash access <access 해 보십시오. http://www.sendmail.org/tips/relaying.html 여기를 참고해 보십시오.