I am using Exchange 2010 and having this issue sending email to external employee's. Internal mail works fine but when sending to external users, I am receiving the following email.. Delivery has failed to these recipients or distribution lists: pete@external.domain.com An error occurred while trying to deliver this message to the recipient's e-mail address. Microsoft Exchange will not try to redeliver this message for you. Please try resending this message, or provide the following diagnostic text to your system administrator. Diagnostic information for administrators: Generating server: mail.domain.com pete@external.domain.com #< #5.0.0 X-Spam-&-Virus-Firewall; host 192.0.0.2[192.0.0.2] said: 554 5.4.6 Hop count exceeded - possible mail loop (in reply to end of DATA command)> #SMTP# Original message headers: X-ASG-Debug-ID: 1282828426-1300-15731-1 Received: from smtp.domain.com ([192.0.0.2]) by mail.domain.com with ESMTP id 6yzeW2gwJ2ODusUE for <pete@external.domain.com>; Thu, 26 Aug 2010 09:13:46 -0400 (EDT) X-Barracuda-Envelope-From: Steve@domain.com X-Barracuda-Apparent-Source-IP: 192.0.0.2 X-Barracuda-UID: pete@external.domain.com - pete@external.domain.com Received: from mail.domain.com (192.0.0.100) by USS-EX1.domain.com (192.0.0.2) with Microsoft SMTP Server id 8.2.254.0; Thu, 26 Aug 2010 08:58:41 -0400 Received: from smtp.domain.com ([192.0.0.2]) by mail.domain.com with ESMTP id EPd3nYelu3xDbE4A for <pete@external.domain.com>; Thu, 26 Aug 2010 08:58:36 -0400 (EDT) Received: from mail.domain.com (192.0.0.100) by USS-EX1.domain.com (192.0.0.2) with Microsoft SMTP Server id 8.2.254.0; Thu, 26 Aug 2010 08:43:31 -0400 Received: from smtp.domain.com ([192.0.0.2]) by mail.domain.com with ESMTP id 55vyozCO3QgGrQW3 for <pete@external.domain.com>; Thu, 26 Aug 2010 08:43:26 -0400 (EDT) Received: from mail.domain.com (192.0.0.100) by USS-EX1.domain.com (192.0.0.2) with Microsoft SMTP Server id 8.2.254.0; Thu, 26 Aug 2010 08:28:21 -0400 Received: from smtp.domain.com ([192.0.0.2]) by mail.domain.com with ESMTP id u0Q2EkcsBN5Rm47o for <pete@external.domain.com>; Thu, 26 Aug 2010 08:28:20 -0400 (EDT) Received: from mail.domain.com (192.0.0.100) by USS-EX1.domain.com (192.0.0.2) with Microsoft SMTP Server id 8.2.254.0; Thu, 26 Aug 2010 08:13:16 -0400 Received: from smtp.domain.com ([192.0.0.2]) by mail.domain.com with ESMTP id Hanzujf0cUA53IVX for <pete@external.domain.com>; Thu, 26 Aug 2010 08:13:15 -0400 (EDT) Received: from mail.domain.com (192.0.0.100) by USS-EX1.domain.com (192.0.0.2) with Microsoft SMTP Server id 8.2.254.0; Thu, 26 Aug 2010 08:12:41 -0400 Received: from smtp.domain.com ([192.0.0.2]) by mail.domain.com with ESMTP id EB2iUgiKjLca6BKZ for <pete@external.domain.com>; Thu, 26 Aug 2010 08:12:40 -0400 (EDT) Received: from mail.domain.com (192.0.0.100) by USS-EX1.domain.com (192.0.0.2) with Microsoft SMTP Server id 8.2.254.0; Thu, 26 Aug 2010 08:12:08 -0400 Received: from smtp.domain.com ([192.0.0.2]) by mail.domain.com with ESMTP id D4z5Hi8BeKOIlB5Q for <pete@external.domain.com>; Thu, 26 Aug 2010 08:12:08 -0400 (EDT) Received: from mail.domain.com (192.0.0.100) by USS-EX1.domain.com (192.0.0.2) with Microsoft SMTP Server id 8.2.254.0; Thu, 26 Aug 2010 08:12:08 -0400 Received: from smtp.domain.com ([192.0.0.2]) by mail.domain.com with ESMTP id 1ExyrTlygnHTROvB for <pete@external.domain.com>; Thu, 26 Aug 2010 08:12:07 -0400 (EDT) Received: from mail.domain.com (192.0.0.100) by USS-EX1.domain.com (192.0.0.2) with Microsoft SMTP Server id 8.2.254.0; Thu, 26 Aug 2010 08:12:07 -0400 Received: from smtp.domain.com ([192.0.0.2]) by mail.domain.com with ESMTP id DF5isNB5v1bi2j9e for <pete@external.domain.com>; Thu, 26 Aug 2010 08:12:06 -0400 (EDT) Received: from mail.domain.com (192.0.0.100) by USS-EX1.domain.com (192.0.0.2) with Microsoft SMTP Server id 8.2.254.0; Thu, 26 Aug 2010 08:12:06 -0400 Received: from smtp.domain.com ([192.0.0.2]) by mail.domain.com with ESMTP id cm7SlHkNuVuC55zw for <pete@external.domain.com>; Thu, 26 Aug 2010 08:12:05 -0400 (EDT) Received: from USS-EX1.domain.com ([192.0.0.2]) by uss-ex1 ([192.0.0.2]) with mapi; Thu, 26 Aug 2010 08:12:05 -0400 From: Steve Woodard <Steve.Woodard@domain.com> To: "Peter Hedberg (ITI)" <pete@external.domain.com> Date: Thu, 26 Aug 2010 08:12:04 -0400 Subject: testing again.. Thread-Topic: testing again.. X-ASG-Orig-Subj: testing again.. Thread-Index: ActFF+VU+QhqAVMQT9OXEq47Y3oCDg== Message-ID: <2AB88EAE19703A4C8A5839986B32D7F39086EC2712@uss-ex1> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: acceptlanguage: en-US Content-Type: multipart/alternative; boundary="_000_2AB88EAE19703A4C8A5839986B32D7F39086EC2712ussex1_

Hi, I have referred a microsoft link and found that the reasons for the issue may be as follows: There is no route for the specified address space. For example, an SMTP connector is configured, but this address does not match. DNS returned an authoritative host that was not found for the domain. The routing group does not have a connector defined. Mail from one server in one routing group does not have a route to another routing group. An SMTP protocol error occurred. You may follow the steps to resolve the issue: Correct the address space, or add an address space of type SMTP with asterisk (*) value to one or more SMTP connectors. Verify that DNS is working correctly. Make sure that the routing groups have connectors that connect them. Regards from www.windowsadmin.info