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NDR - 550 Unrouteable address when sending to *@inbox.ru

Posted on 2008-06-09
Medium Priority
Last Modified: 2010-04-21

Users from my Exchange server are receiving the following NDR when trying to send an email to *@inbox.ru:

Delivery has failed to these recipients or distribution lists:

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.

The following organization rejected your message: abc.mail.ru.


Sent by Microsoft Exchange Server 2007

Diagnostic information for administrators:

Generating server: mymailserver.mydomain.com

abc.mail.ru #550 Unrouteable address ##


I went to www.dnsstuff.com and did a DNSReport on my domain and I noticed this warning from the report:

WARNING: One or more of your mailservers is claiming to be a host other than what it really is (the SMTP greeting should be a 3-digit code, followed by a space or a dash, then the host name). If your mailserver sends out E-mail using this domain in its EHLO or HELO, your E-mail might get blocked by anti-spam software. This is also a technical violation of RFC821 4.3 (and RFC2821 4.3.1). Note that the hostname given in the SMTP greeting should have an A record pointing back to the same server. Note that this one test may use a cached DNS record.

mydomain.com.inbound15.mxlogic.net claims to be non-existent host p02c11m117.mxlogic.net: <br /> 220 p02c11m117.mxlogic.net ESMTP mxl_mta-5.5.0-3 [3164842928.125256.00-025]; Mon, 09 Jun 2008 16:06:45 -0600 (MDT); NO UCE, INBOUND <br />

Could the warning pasted above be why the organization abc.mail.ru rejected the message? Or is the problem with the unroutable address?

Question by:McCoyIT
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Expert Comment

ID: 21747403
hmm it sounds like (from the NDR message) that their records for your *@inbox.ru are not in their routing table... so more likely a problem on their side..
have you tried sending them a message from a different email server (like from gmail.com?)
if they can receive that message than you know its your exchange server's problem.

Author Comment

ID: 21747408
I did try from my Gmail account and I did not get a bounce back, so it is my Exchange server.
LVL 25

Expert Comment

ID: 21748750
The DNSReport test fails pretty dismally when you are not receiving mail directly.

Send an email from your exchange server to your GMail account and then post the headers of that here - then we can see what is going on.
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Author Comment

ID: 21751645
Below is the message header from my account on the Exchange server to my Gmail account.

Delivered-To: mygmail@gmail.com
Received: by with SMTP id k8cs236250rve;
        Mon, 9 Jun 2008 12:26:29 -0700 (PDT)
Received: by with SMTP id l3mr1614865wff.174.1213039587576;
        Mon, 09 Jun 2008 12:26:27 -0700 (PDT)
Return-Path: <me@mydomain.com>
Received: from myexternal.domain.com (static-xxx-xxx-xxx-xxx.ptr.terago.net [xxx.xxx.xxx.xxx])
        by mx.google.com with ESMTP id 24si11581716wfc.3.2008.;
        Mon, 09 Jun 2008 12:26:27 -0700 (PDT)
Received-SPF: neutral (google.com: xxx.xxx.xxx.xxx is neither permitted nor denied by best guess record for domain of me@mydomain.com) client-ip=xxx.xxx.xxx.xxx;
Authentication-Results: mx.google.com; spf=neutral (google.com: xxx.xxx.xxx.xxx is neither permitted nor denied by best guess record for domain of me@mydomain.com) smtp.mail=me@mydomain.com
Received: from myinternal.domain.com ([xxx.xxx.xxx.xxx]) by myinternal.domain.com
 ([xxx.xxx.xxx.xxx]) with mapi; Mon, 9 Jun 2008 13:26:27 -0600

Was doing some more digging around and I noticed that my mail server name for HELO or EHLO responses is my external FQDN, but on the DNSreport the warning was for, myexternalFQDN.com.inbound15.mxlogic.net; which is my smart host which filters all my inbound email.

Am I suppose to have mydomain.com.inbound15.mxlogic.net in the HELO or EHLO field of my send connector?
LVL 25

Expert Comment

ID: 21755275

Is that a correct address?  Does it resolve to your IP address?

The other problem, which is pretty major, is that your reverse DNS entry is "ugly" - it exists, but it looks bad, so a lot of places will reject your mail.  You need to call your ISP and get them to change it from static-xxx-xxx-xxx-xxx.ptr.terago.net to myexternal.domain.com


Author Comment

ID: 21779834
Sorry for the delay, yes it does resolve.  For example if I were to mail.mydomain.com it will resolve to the correct address.  Any thoughts on the DNS Report warning message?  

Author Comment

ID: 21779846
For the example I meant to type "...if I were to ping mail.mydomain.com..."
LVL 25

Accepted Solution

kieran_b earned 2000 total points
ID: 21782900
>>Any thoughts on the DNS Report warning message?  

Ignore it - it only makes sense if you receive and send mail directly.  You don't need to change the SMTP Greeting of your server to match MX Logic

>>Received: from myexternal.domain.com (static-xxx-xxx-xxx-xxx.ptr.terago.net [xxx.xxx.xxx.xxx])

That shows you have a correct SMTP Greeting - but a poor rDNS entry.  Talk to your ISP and tell them you want your rDNS entry changed from static-xxx-xxx-xxx-xxx.ptr.terago.net to myexternal.domain.com

Author Comment

ID: 21782952
I will talk to my ISP and ask them to change it.  I just want to clarify the myexternal.domain.com is my exchange server's external FQDN name.
LVL 25

Expert Comment

ID: 21783039
>>I just want to clarify the myexternal.domain.com is my exchange server's external FQDN name.

That was my understanding.

While you are waiting, you can test out DNS queries from your server;

On the exchange server,
Start > run > cmd
set type=mx

Does it bring up the following?
Non-authoritative answer:
inbox.ru        MX preference = 10, mail exchanger = mxs.mail.ru

Cancel out of nslookup (CRTL + C)
then type;
telnet mxs.mail.ru 25
Does it connect?

Author Comment

ID: 21783102
Yup, connects fine.

Author Closing Comment

ID: 31465584
The ISP made the change today, and I don't receive that bounce back anymore, but I do receive a bounce back for a non existent mailbox.  So it looks like it worked, the problem was there was no mailbox for that user.


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