451 DNS Query Failed error in Exchange 2007
We are having trouble sending email to one particular domain. This is using Exchange 2007 on a Windows SBS 2008 box. Only server at our site, only problem we have seen with email in 6 months since it was implemented. I am receiving a 451 4.4.0 DNS query failed error when trying to send to the domain polytronix.com . From the Exchange server I can telnet to the client's mail server and receive a HELO. NSLookup gives the following: C:\Windows\system32>nslookup -type=mx polytronix.com Server: UnKnown Address: fe80::23c8:9a82:d40b:251a Non-authoritative answer: polytronix.com MX preference = 10, mail exchanger = mail.polytronix.com polytronix.com MX preference = 20, mail exchanger = mail.polytronix.com mail.polytronix.com internet address = 72.16.238.22 mail.polytronix.com internet address = 72.16.238.22 I am waiting to hear back from the customer as I am no longer sure the IP from the NSLookup is correct (customer stated the IP was 72.16.238.18, not 22). Anyone have any other ideas on how I can troubleshoot/resolve this issue? Thanks in advance!
October 19th, 2009 5:25pm

Hi,Please try to send the email by using telnet to narrow down the cause.http://support.microsoft.com/kb/153119If you can send the email by using the telnet, this indicates the client's mail server doesn't block your email address. Then you need to create a separate send connector and set the client's mail server as the smarthost to send the email. Through this we can confirm whether the DNS is the cause of the issue. If that is the DNS issue, you need to check the "Use the External DNS Lookup settings on the transport server" option or update the MX record of the particular domain.ThanksAllen
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October 21st, 2009 11:37am

OK I did confirm with the customer (Polytronix.com) that the IP in the NSLookup was correct so I can rule that out now. Here is the results of my telnet with their mail server at mail.polytronix.com. Not sure if I did this right because the tutorial was very ambiguous - was I supposed to send the email to myself or to the customer @ Polytronix? In either case it took me a while to get this to go through - every other session instead of returning 250 for these commands it would give me a bevy of other error messages (things like bad command, unknown address, and my session was killed a few times by a lost connection from their server). 220 beta.Polytronix.com Microsoft ESMTP MAIL Service ready at Wed, 21 Oct 2009 0 8:28:51 -0500 EHLO 250-beta.Polytronix.com Hello [67.52.2.58] 250-SIZE 250-PIPELINING 250-DSN 250-ENHANCEDSTATUSCODES 250-STARTTLS 250-X-ANONYMOUSTLS 250-AUTH NTLM 250-X-EXPS GSSAPI NTLM 250-8BITMIME 250-BINARYMIME 250-CHUNKING 250-XEXCH50 250 XRDST MAIL FROM:amartin@tg3electronics.com 250 2.1.0 Sender OK RCPT TO:lshedenhelm@polytronix.com 500 5.3.3 Unrecognized command RCPT TO:lshedenhelm@polytronix.com 250 2.1.5 Recipient OK DATA 354 Start mail input; end with <CRLF>.<CRLF> Subject:test message via telnet This is a test message sent via mail.polytronix.com over telnet to help troubles hoot TG3 Electronics email problem with Polytronix. . 250 2.6.0 <86d32082-944a-4647-8ccf-48982fb35226@beta.Polytronix.com> Queued mail for delivery quit 221 2.0.0 Service closing transmission channel I will look for instructions on the proper way to create the send connector you are talking about, but if you have details on how to do that it would help greatly. Thanks!
October 21st, 2009 4:41pm

Hi,Yes, you need to send the email to the customer@ploytronix.com from your email address. From the information, it seems that you can send the email without no issue. This indicates the remote server is openning for your email address.The possible cause is the DNS issue. Now please check the "Use the External DNS Lookup settings on the transport server" optionon the current Send Connector to examine whether you can send the email normally.ThanksAllen
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October 22nd, 2009 1:22pm

Thanks that works! Would not have found that setting on my own.
October 22nd, 2009 5:42pm

Hi,Glad to hear that is working.ThanksAllen
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October 23rd, 2009 5:49am

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