Thanks In Advance...

Need help to identify a Critical Issue in Live Environment. 

We have Setup a Email server for out organization domain.com which is working properlly and the mail flow is also works fine with other domain. Since last week we observe that one of our client company based in UK complain that they are unable to send mails to our domain. 

We start investigating and found that some mails are coming properly and some are don't even hit out Trend Micro Mail Gateway server. After 6 Hrs client get the NDR over return receipt. 

Our Enviorment :-

Domain :- Domain.com

MX:- 11.12.124.15 & 200.225.112.23 (mail.domain.com) Preference 10

11.12.1247.16 & 200.225.112.24 (Gateway.domain.com) Preference 20

11.12.124.17 & 200.225.112.25 (relay.apeejaygroup.com) Preference 30

Mail Gateway Appliance :- Trend Micro InterScan Messaging Security Gateway 9.0

Client Environment:-

Domain :- clientdomain.com

MX :- brightmail by Symantec Messagelabs Cloud. 

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When Client sent a mail it don't even hit any of our mail gateway server. But the user gets the Non Delivery Message. In from Brightmail NDR following error message is showing.

Delivery attempt failure - transient Attempted delivery 71/31-01753-DD55DE55 to 11.12.124.15 on Mon Sep 7 09:36:23 2015 Error Message: "451 4.4.2 [internal] send HELO/EHLO failed" Providing this log to the recipient, hopefully they would be able to explain this answer when we try to connect to their Server 11.12.124.15

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Need help to identify that where is the issue and how to fix this so that we can start communication between our client over mail smoothly. 

Symantec reports that this could be an issue with an email loop: https://support.symantec.com/en_US/article.TECH131314.html. 

Have you checked to see whether your Trend mail gateway is reporting any performance issues? Check the SMTP logs on the Trend mail gateway to find out more information on failed connections.

Thanks.

Hi Mark,

Can you please describe what is email loop. And how to fix this. 

Thanks in advance.