메일 송신이 안되요

수신은 되는데 송신만 하면 다음과 같은 에러가 납니다. 서버에 문제가 있는지 ㅠㅠ

The original message was received at Thu, 23 Mar 2006 19:15:11 +0900
from 
   ----- The following addresses had permanent fatal errors -----
<xxxx@xxxx.xx>
    (reason: 550 Host unknown)

   ----- Transcript of session follows -----
550 5.1.2 <xxxx@xxxx.xx>Host unknown (Name server: smtp.burberry.co.kr: host not found)