메일계정생성 후 오류리턴메일

메일계정을 생성(useradd로생성)하고나서 메일을 보냈더니
리턴메일이 돌아왔습니다. zone파일에서 설정이 잘못 된건가요?
아니면 sendmail.cf 설정이 잘못된건가요?

############### 아래는 쉘프롬프트에서 보낸후 리턴메일 ##############
The original message was received at Thu, 12 May 2005 10:41:32 +0900 
from localhost.localdomain [127.0.0.1]
   ----- The following addresses had permanent fatal errors ----- 
<abc at test-d.co.kr>  (reason: 553 5.3.5 system config error)
   ----- Transcript of session follows -----
553 5.3.5 test-d.co.kr config error: mail loops back to me (MX problem?)
554 5.3.5 Local configuration error

################## 아래는 아웃룩에서 보낸후 리턴메일 ###############
The original message was received at Thu, 12 May 2005 10:10:41 +0900 
(KST) from [210.124.214.183]

   ----- The following addresses had permanent fatal errors ----- 
<abc at test-d.co.kr>
    (reason: 550 5.7.1 <abc at test-d.co.kr>... Relaying denied)

   ----- Transcript of session follows ----- ... while talking to 
plusyou.com.:
>>> RCPT To:<abc at test-d.co.kr>
<<< 550 5.7.1 <abc at test-b.co.kr>... Relaying denied 550 5.1.1 <abc@test-
b.co.kr>... User unknown