메일을 보내면.. 잘 전송되었다고 나오고요..

나중에 제 보낸 메일로
!Nmail Send error 550 5.1.1 ... User unknown
이런 제목으로 리턴됩니다.
내용은
Error Message : 550 5.1.1 ... User unknown

-- You SendMail --

>> Received: from mail.asppro.net (211.239.117.18)
>> by asppro.net (211.239.117.18) with [Nmail V3.2 20020608(S)]
>> for from ;
>> Thu, 26 Sep 2002 09:01:55 +0900
>> From: =?ks_c_5601-1987?b?sPy4rsDa?=
>> Subject: =?ks_c_5601-1987?b?tOvIo8ioxuTAzMH2IMDMwPy/z7fhIMffvcC0z7TZLg==?=
>> To: ****@****
>> MIME-Version: 1.0
>> X-Mailer: SM
>> Date: Thu, 26 Sep 2002 09:01:55 +0900
>> Content-Type: text/html; charset=euc-kr
>> Content-Transfer-Encoding: 8bit

이렇게 되어있네여..

왜 그럴까여"???