Today we started having this problem with a external domain that has been working fine before. This is not happening to all emails or all domains.
Last week there was problem with a co.uk domain and that went away by itself (i know...)
I've done the tests with Mxtoolbox and exchange connectivity and they all pass.
The Exchange 2013 server forwards to Smarthost (GFI)
Server Exchange 2013
Clients: outlook 2010/2013
Diagnostic information for administrators:
Generating server: myserver.mydomain.com
user@externaldomain.com
Remote Server returned '< #5.5.0 smtp;550-Please turn on SMTP Authentication in your mail client. >'
Original message headers:
Received: from myserver.mydomain.com ([10.0.0.16] RDNS failed) by myserver.mydomain.com
with Microsoft SMTPSVC(7.5.7601.17514); Wed, 17 Jun 2015 11:42:42 -0700
Received: from EMSRV.WL.local (10.0.0.16) by EMSRV.WL.local (10.0.0.16) with Microsoft SMTP
Server (TLS) id 15.0.1044.25; Wed, 17 Jun 2015 11:38:34 -0700
Received: from EMSRV.WL.local ([fe80::4096:a0c:3cef:13c0]) by EMSRV.WL.local ([fe80::4096:a0c:3cef:13c0%15])
with mapi id 15.00.1044.021; Wed, 17 Jun 2015 11:38:34 -0700
From: myUser
To: External user
Subject: K
Thread-Topic: K
Thread-Index: AdCpLMPIwf2IRxL0TEmNJMzqXdSUGg==
Date: Wed, 17 Jun 2015 18:38:34 +0000
Message-ID: <459b7995e3d243ad93a61a0f1da9ff73@EMSRV.WL.local>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach: yes
X-MS-TNEF-Correlator:
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: [10.0.0.48]
Content-Type: multipart/related;
boundary="_007_459b7995e3d243ad93a61a0f1da9ff73EMSRVWLlocal_";
type="multipart/alternative"
MIME-Version: 1.0
Return-Path: MyUser@mydomain.com
X-OriginalArrivalTime: 17 Jun 2015 18:42:42.0971 (UTC) FILETIME=[652B66B0:01D0A92D]
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