DAG and availability issues

Hi All,

I'm new to all this Exchange stuff - I am currently experiencing an issue with DAG availability and receiving external emails - I think these two issues may be related somehow.

First off, let me give some background.

The site has a DC, Exchange (running 2010 - couldnt find the right forum for this version of Exchange) and RDS server (Server 2008R2) all connected to the same domain.

Users log in and access their emails via RDS server - has been running fine since this has been originally set up.

Recently, we built a server for a new site this business has just opened, and set up a secondary DC, RDS and Exchange server - fairly basic stuff - DFS replication between the two sites which are connected via an IPsec VPN, still connected to the same domain.

Since we set up DAG between the two Exchange servers, we have intermittent issues with receiving external emails to the users' mailboxes - both at the original site and the second site (MX records still point back to the original site).

These messages appear to be getting stuck in the 'hub version 14' queue (as reported by the queue viewer in EMC). It reports the error as "451 4.4.0 DNS Query Failed. The error was: SMTPSEND.DNS.NonExistentDomain; nonexistent domain"

The only way to get these messages through is to restart the original exchange server - they then go through without issue. but only for a while - the issue comes back again later on throughout the day.

This issue has only been happening since the deployment of the DAG config - the mailbox copies appear to be fine - primary site says its connected, secondary site says healthy.

The other issue I am seeing - which is why im not sure if its related - is while the primary Exchange server is restarting, outlook loses connectivity to exchange altogether - It was my understanding that the DAG configuration should move the database over to the secondary site and keep its outlook clients connected - which is the whole point of this config.

Is there something I may have missed?

May 11th, 2014 9:47pm

Hi 

Here you go

http://msexchangeguru.com/2013/11/23/451-4-4-0-dns-query-failed-the-error-was-smtpsend-dns-nonexistentdomain-nonexistent-domain/

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May 12th, 2014 1:04am

Hi,

I recommend you follow the suggestions mentioned in the link provided by Sathish above to check the result.

Make sure the DNS records are configured correctly.

If the issue persists, please use the Get-MailboxDatabaseCopyStatus and Test-ReplicationHealth cmdlet to test against the DAG.

And please check the application log on the Mailbox server where the messages are queued to see if there is any related events.

Best regards,
Belinda

May 13th, 2014 1:38am

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