SPF 필터는 발송자의 DNS 설정값을 조회해서 값이 설정되지 않았거나 잘못 설정된 경우에 메일을 거부하는 필터 입니다.
보통 메일교환기 (MX) 값이 잡혀 있지 않거나 역방향 조회쪽에 호스트가 등록되어 있지 않아서 발생합니다.
DNS 서버 설정 부분을 점검해 보십시오.

김철희 님이 쓴 글입니다.
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:※ 필수입력정보 ※
:
:▷ 제품버젼 : nWmail (Standard Ver3.5) – Virus wall
:▷ 사용중인 주소(URL) : http://
:▷ 문제발생시 메뉴/주소 :
:▷ 문제발생시 에러메세지
:: Fw: !Nmail Send error 451 SPF lookup failure (#4.3.0)
:
:▷ 질문내용
:: 이런 메세지를 받았는데 어떤 문제인가요 ?
: 중요한 업무 메일입니다.
: 하단은 받은 메일 내용입니다.
:
:Untitled ADRIAN LEE / BRANCH MANAGER Global Partners Logistics USA inc.
:11099 South. La cienga suit 262 Los Angeles CA 90045 E-mail :
:****@**** Tel : 1-310-337-0020 Fax :
:1-310-337-0097 -------------------------------------------------------------
:------------- Please visit our home : http://www.globalgpl.com- On-line
:cargo tracing service and much more !
:----- Original Message -----
:From: "dsecargonet.com PostMaster" <****@**** >
:To: <****@**** >
:Sent: Monday, October 18, 2004 6:58 PM
:Subject: !Nmail Send error 451 SPF lookup failure (#4.3.0)
:
:
: >
: > Error Message : 451 SPF lookup failure (#4.3.0)
: >
: > -- You SendMail --
: >
: > > > Received: from notebook (64.164.253.2)
: > > > by dsecargonet.com (203.242.142.129) with [Nmail V3.51 20040105(S)]
: > > > for <****@**** > from <****@**** >;
: > > > Tue, 19 Oct 2004 10:56:14 +0900
: > > > Message-ID: <009501c4b580$45ced240$****@**** >
: > > > Reply-To: "Adrian Lee" <****@**** >
: > > > From: "Adrian Lee" <****@**** >
: > > > To: "=?ks_c_5601-1987?B?x+PAscG+tOu4rrTUXChMRyBCUkFaSUxcKQ==?="
:<****@**** >
: > > > Cc: "=?ks_c_5601-1987?B?sejBvr/twMy757TUXChEU0VcKQ==?="
:<****@**** >,
: > > > "=?ks_c_5601-1987?B?sei/tcHYwvfA5bTUXChEU0VcKQ==?="
:<****@**** >,
: > > > =?ks_c_5601-1987?B?wMzBvr/su+fA5bTUXChTUEVYL0JSQVpJTFwp?=
:<****@**** >,
: > > > =?ks_c_5601-1987?B?wMyw5rz2tNRcKERTRVwp?= <****@**** >,
: > > > "=?ks_c_5601-1987?B?w6S47bHiu+fA5bTUXChkc2VcKQ==?="
:<****@**** >,
: > > > "=?ks_c_5601-1987?B?x8/H/cH4sPrA5bTUXChMRyBCUkFaSUxcKQ==?="
:<****@**** >
: > > > Subject: =?ks_c_5601-1987?B?RmxpZ2h0IERlbGF5ILDH?=
: > > > Date: Mon, 18 Oct 2004 19:06:34 -0700
: > > > MIME-Version: 1.0
: > > > Content-Type: multipart/mixed;
: > > > boundary="----=_NextPart_000_0090_01C4B545.95B8BEA0"
: > > > X-Priority: 3
: > > > X-MSMail-Priority: Normal
: > > > X-Mailer: Microsoft Outlook Express 6.00.2800.1409
: > > > X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1409
: > > >
: > > > This is a multi-part message in MIME format.
: > > >
: > > > ------=_NextPart_000_0090_01C4B545.95B8BEA0
: > > > Content-Type: multipart/related;
: > > > type="multipart/alternative";
: > > > boundary="----=_NextPart_001_0091_01C4B545.95B8BEA0"
: > > >
: > > >
: > > > ------=_NextPart_001_0091_01C4B545.95B8BEA0
: > > > Content-Type: multipart/alternative;
: > > > boundary="----=_NextPart_002_0092_01C4B545.95B8BEA0"
: