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5.1.2 SMTP; 550 Host unknown - Email Bounce

Posted on 2016-09-14
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Last Modified: 2016-10-18
Hi Guys,

First time I have posted in here so be nice :)

5.1.2 SMTP; 550 Host unknown

one of my customers is having email bounce back issues, have done multiple checks with RBL and other , nothing is coming up blocked.

Current server is a SBS 2011 with exchange 2010. it doesn't happen to every email only some and has got me stumped as to why this is happening .
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Question by:Michael Perry
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Assisted Solution

by:Elizabeth Anderson
Elizabeth Anderson earned 200 total points (awarded by participants)
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If you're getting an 550 error then it generally means the e-mail address is bad, or in the example above the mailbox has been suspended.  Any mail server will just bounce these messages.
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by:Dr. Klahn
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Microsoft says:

The SMTP 5.1.2 error code is received when one of the servers on the way to the destination is unable to resolve the domain name of a recipients email address. Said differently: one of the servers on the way to the destination, including your server or your ISP, has a DNS problem or, possibly correctly, does not like one of the email addresses in the message’s TO, CC and BCC fields.

This error may not be occurring at your site.  It is occurring at the last SMTP server that relayed the mail on the way to its target.  Expand the headers of the returned message fully, and see at what site the problem is occurring.  Alternatively the bounce message may contain that information.

If you don't know how to get that info, post the entirety of the bounce message here and we can see what looks likely.
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Author Comment

by:Michael Perry
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this is the bounce messege, i have removed the useres address

Diagnostic information for administrators:

Generating server: mx0a-00185f01.pphosted.com

user@user
user@user #<iphotels.com.au #5.1.2 SMTP; 550 Host unknown> #SMTP#

Original message headers:

Return-Path: <NH94@ntrs.com>
Received: from pps.filterd (m0049146.ppops.net [127.0.0.1])  by
 mx0a-00185f01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id u861mjlb025784;
        Mon, 5 Sep 2016 20:50:15 -0500
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ntrs.com; h=from : to : cc : subject
 : date : message-id : references : in-reply-to : content-type :
 mime-version; s=2016-07-05-ntrs;
 bh=picdFRR/u819ptq2WCHm4Oa5C90oleQJ7r+wGI5vNKk=;
 b=Zzj2C2pGVbLZ5+oEd2PEh6CUNvIsOuedyNfes8fcuJNSE3eEnjPXlcKkyusNJPXJEz1T
 InBNptuHyPCwE3C3hAEPy/WY/k8kcMhXu2oi19h/aEnrF0U9uhPZP0VjoLfkQ3veNzy1
 E1rLQTF5lVs8fL1fKGlaAOB0v2upa/mLOJkFx7JN3jilESMiTHgd8j+v1IzCF0nNnHIY
 oPbhimjuS7e44mKJYYr9hX0hLhf8tfKlbliC1ze1m4NOMmvsi02CbisZcMekX6LGH9oj
 K2BhBmmGmZwsu6keutYAYtSfE3KAxeq5gUkvuhiBHJa7OFNsCJRF9AVCe6t9fPe3MRYS RQ==
Received: from appwpcupmta03.ntrs.com (extmail.ntrs.com [208.95.148.124])   by
 mx0a-00185f01.pphosted.com with ESMTP id 259c2dhkgk-1       (version=TLSv1.2
 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT);    Mon, 05 Sep 2016
 20:50:15 -0500
Received: from pps.reinject (appwpcupmta03.ntrs.com [127.0.0.1])     by
 appwpcupmta03.ntrs.com (8.15.0.59/8.15.0.59) with ESMTPS id u861oDoN013955
        (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT);
        Mon, 5 Sep 2016 20:50:13 -0500
Received: from appwpcupmta03.ntrs.com (appwpcupmta03.ntrs.com [127.0.0.1])  by
 pps.reinject (8.15.0.59/8.15.0.59) with SMTP id u861oDwP013949;     Mon, 5 Sep
 2016 20:50:13 -0500
Received: from appnpcupmta15.ntrs.com ([10.33.29.147])       by
 appwpcupmta03.ntrs.com with ESMTP id u861oCYG013947; Mon, 05 Sep 2016
 20:50:13 -0500
Received: from SDCMXSP70.ent.ad.ntrs.com (sdcmxsp70.ent.ad.ntrs.com
 [10.90.23.13]) by appnpcupmta15.ntrs.com (8.15.0.59/8.15.0.59) with ESMTP id
 u861oCpp030978;       Mon, 5 Sep 2016 20:50:12 -0500
Received: from WPCMXSP95.ent.ad.ntrs.com (10.33.146.3) by
 SDCMXSP70.ent.ad.ntrs.com (10.90.23.13) with Microsoft SMTP Server (TLS) id
 14.3.210.3; Mon, 5 Sep 2016 20:50:12 -0500
Received: from SGTMMXSP17.ent.ad.ntrs.com (10.196.80.2) by
 WPCMXSP95.ent.ad.ntrs.com (10.33.146.3) with Microsoft SMTP Server (TLS) id
 14.3.210.3; Mon, 5 Sep 2016 20:50:11 -0500
Received: from SGTMMXSP16.ent.ad.ntrs.com ([169.254.4.48]) by
 SGTMMXSP17.ent.ad.ntrs.com ([10.196.80.2]) with mapi id 14.03.0210.003; Tue,
 6 Sep 2016 09:50:07 +0800
From: Neil Hetherington <NH94@ntrs.com>
To: user@user
CC: user@user
Subject: RE: Robb 2000's rugby reunion
Thread-Topic: Robb 2000's rugby reunion
Thread-Index: AdHXUQODyMn5HBlkQXKQvcyyAF38sQA4oIOuAAc7htYAEtG8FAvACDaAABEcstA=
Date: Tue, 6 Sep 2016 01:50:06 +0000
Message-ID: <FAAC4CF607F32342A6A1D5DD92422CCB02A85F1E@SGTMMXSP16.ent.ad.ntrs.com>
References: <SY3PR01MB07777ACBBB2B03CA4177B6D38B3A0@SY3PR01MB0777.ausprd01.prod.outlook.com>
 <20160707093955.6148182.83330.6157@rabobank.com>
 <C4764D45-666F-4A1E-89E3-16DB55412C6A@maccalluminglis.com.au>
 <A01B6C48-7B71-4FBC-A0C7-9D55C1D5C356@nab.com.au>
 <CAP-v-kBW7-z_=ocLT+d_FWfdNNT2J3TbnuEnrjhpYkCghhVS4w@mail.gmail.com>
In-Reply-To: <CAP-v-kBW7-z_=ocLT+d_FWfdNNT2J3TbnuEnrjhpYkCghhVS4w@mail.gmail.com>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-sensitivitylevel: 4UC-11
x-ntaclog: 4UC-11201609061150nh94;4UC-11201609061150SSender
x-originating-ip: [10.197.78.11]
Content-Type: multipart/alternative;
        boundary="_000_FAAC4CF607F32342A6A1D5DD92422CCB02A85F1ESGTMMXSP16entad_"
MIME-Version: 1.0
X-CFilter-Loop: Reflected
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-09-05_11:,,
 signatures=0
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 suspectscore=0
 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011
 impostorscore=0 lowpriorityscore=0 adultscore=0 classifier=spam adjust=0
 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1609060027
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Accepted Solution

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Dr. Klahn earned 300 total points (awarded by participants)
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Thanks for the update.  The reason the email is failing is because there is no domain registered with the name "iphotels.com.au".  That being the case, "5.1.2 SMTP; 550 Host unknown" is correct although perhaps a bit obscure.

No such domain exists
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Expert Comment

by:Dr. Klahn
Comment Utility
EE email requested stale question closure.
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