451 4.4.0 DNS query failed - NonExistentDomain (Full Version)

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pangjoe -> 451 4.4.0 DNS query failed - NonExistentDomain (26.Mar.2014 11:58:00 AM)

I am in the process of migrating from Exch 2007 to 2013 for a small company. It is a very simple setup of just a single domain which has 1 server, 1 organization and 1 database. Here is what I have done so far:

1. Installed a physical server EX13 for Exchange 2013 with SP1. All updates have been applied.

2. Added a new Receive Connector of EX13 in addition to existing EX07.

3. Changed SMTP port forwarding on the firewall from EX07 to EX13.

4. Migrated a few mailboxes to the EX13.

Accounts on both servers have no issues with exchanging email both ways on the Internet. However, when accounts on the old server email to migrated users, the new server does not always receive the messages promptly. There is a delay as much as 30 minutes that happens sporadically.

I checked the message header on the delayed messages and found that they had been stuck in EX07 for a long time before forwarding to EX13. From Ex07 queue viewer, I found the following error:

451 4.4.0 DNS query failed. The error was: SMTPSEND.DNS.NonExistentDomain; nonexistent domain

Net Hop Domain: hub version 15
Delivery type: SMTP Relay in Active Directory
Message Source Name: FromLocal
Last Error: 451 4.4.0 DNS query failed. The error was: SMTPSEND.dns.NonExistentDomain;nonexistentdomain

The status showed "retry" and eventually the message would be delivered. Once it went through, I sent another one again from an EX07 account to EX13 account, the message was received instantly.

So far I have tried the following:

1. Added a host entry to point EX13.my_external_domain.com to the internal address of EX13

2. Added an 'A' record on the internal DNS server with the same entry.

3. Verified that EX13.my_external_domain.com was accessible from EX07 using this FQDN.

4. Removed EX07 and leaving only EX13 on the Receive Connector list

5. Removed EX13 and leaving only EX07 on the Receive Connector list

6. Put both connectors back

There is no change of status. Every morning our users are saying that they could not email users on the new server. Then after 30 minutes, the problem disappeared but it will come back later in the day. On the other hand, users on the new server do not notice any delay when sending messages to the those on the new box. At this point, I don't feel comfortable migrating more users. Can someone please shed some lights?

ronniepaul -> RE: 451 4.4.0 DNS query failed - NonExistentDomain (22.Jan.2015 3:55:06 AM)


Once a while i was also facing the same issue. Go through the link to know about the error "451 4.4.0 DNS query failed"



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