자세히는 모르겠지만 서버가 릴레이서버로 이용당하는것 같네요.
 http://kldp.org/KoreanDoc/Virtual_Service-KLDP 문서에서
 /etc/sendmail.cf 와
/etc/mail/access 설정을 확인해보십시요.
 4-3 절과 4-6 절에 있습니다.
  : 이런 메일이 와써요
: 대처 방법은 없는가요? 서버에서 할수 잇는 최선의 방법은요
: 누가 하는 걸까요.. 알려주시고 서버에서 할수 있는 방법과
: 대처 방법좀 알려주세요
:
:
: --------------내                 용------------------------------
: I recently received the following message, which appears to be from one of
: your users or was relayed by one of your machines.  It looks to me like a
: spam, unsolicited commercial e-mail.  Such mail is very annoying and widely
: considered to be abusive.
:
: If your domain is the source for this E-mail, could you encourage him/her/it
: to cut it out?  Thanks.
:
: If you are one of the relays down the chain, maybe you should consider to
: restrict the use of your mail-server? Thanks.
:
: If your host was faked or in any way spoofed, I trust you would still like to
: know about it. Please regard this mail as information rather than
: accusation. Forged headers are unfortunately sometimes used and you may have
: received this mail even though you're completely innocent.
:
: If you know who to tell or inform about this in order to make it stop. Please
: forward this information to whom it may concern.
:
: (This mail was automatically generated.)
:
: --- start of spam ---
: Return-Path:<winfriedp at stwimst.at>
: Received: from dolly1.pobox.com (IDENT:postfix at dolly1.pobox.com [208.210.124.91])
:  by equinox.graphitebox.com (8.11.0/8.8.7) with ESMTP id f0T44AC21769
:  for <ahknight at graphitebox.com>; Sun, 28 Jan 2001 22:04:11 -0600
: Received: from dolly1.pobox.com (localhost.localdomain [127.0.0.1])
:  by dolly1.pobox.com (Postfix) with ESMTP
:  id F32DA2BF0B; Sun, 28 Jan 2001 23:04:04 -0500 (EST)
: Received: from dns.ibzone.net (unknown [203.229.6.25])
:  by dolly1.pobox.com (Postfix) with ESMTP
:  id 7A1FC2BF4C; Sun, 28 Jan 2001 23:02:59 -0500 (EST)
: Received: from kcx-ks18a-183.rasserver.net_[205.185.0.183] (kcx-ks18a-183.rasserver.net [205.185.0.183])
:  by dns.ibzone.net (8.9.3/8.9.3) with SMTP id NAA08101;
:  Mon, 29 Jan 2001 13:02:08 +0900
: From: winfriedp at stwimst.at : Received: from gulp.datacom.de by kcx-ks18a-183.rasserver.net with ESMTP; Sun, 28 Jan 200
: 1 22:58:47 -0600 Message-ID:<000003b115fd$00005143$00004c3f at gulp.datacom.de>
: To:<howard at 5Business.cc>
: Subject: [spam score 10.00/10.0 -pobox] 100% return in 90 days!!                         19519
: Date: Sun, 28 Jan 2001 22:58:43 -0600
: MIME-Version:1.0
: Content-Type: text/html;
:  charset="iso-8859-1"
: Content-Transfer-Encoding: quoted-printable
: X-Priority: 3
: X-MSMail-Priority: Normal
: Reply-To: johnboy at 5Business.cc : X-Mailer: QUALCOMM Windows Eudora Version 4.3.2
: Status: RO
: X-Status:
: X-Keywords:              
: X-UID: 9--이글을 읽는 모든이에게 평화가 함께 하기를.. ^^;;