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Emails from Exchange 2010 to Exchange 2013 showing in Unreachable Queue

    Question

  • I have installed Exchange 2013 in the Exchange 2010 environment and created some test users and didn't notice any issues.

    After initial testing I have moved some of the production mailboxes from Exchange 2010 to Exchange 2013, intermittently i see that emails from Exchange 2010 users for Exchange 2013 users are stuck on Exchange 2010 HUB servers in a Unreachable Queue.

    Initially it was showing DNS error , SMTP SEND error in the Last Error, but now it doesn't show anything and the emails sit in Unreachable Domain.

    I checked different DNS options etc, it only works when I bounce the AD Topology Service on the HUB Server.

    After bouncing the service if i check, then i can see the "Hub Version 15" queue showing and the emails are delivered to the Exchange 2013 mailboxes.

    Not sure what is causing the problem as I checked both the Exchange 2010 and Exchange 2013 servers are in the same subnet and also they are in Same AD Site.

    Can anyone helpme with this, i cannot proceed with the migration before I resolve this issue.


    mdimthyas

    Monday, November 21, 2016 11:34 AM

All replies

  • On Exchange 2010 did you create a receive connector pointing to Exchange 2013? With auth on Exchange server checked?
    Monday, November 21, 2016 10:42 PM
  • No, i am using the default connectors, i didnt create any connectors and as i mentioned, its intermittent, emails are flowing fine, only sometimes it goes to Unreachable Domain.

    mdimthyas

    Tuesday, November 22, 2016 4:17 AM
  • Can you create one on both side as a dedicated connector and see if it work? If it does then the default connectors has some sort of timeout connection.
    Wednesday, November 23, 2016 4:59 AM
  • Hi,

    What's the version of SP/CU for exchange 2010/2013 in your environment?

    And when messages are stuck in the Unreachable Queue, please review application log to see if there are any error events, especially for "Source: MSExchange ADAccess"

    Meanwhile, make sure all the other required Exchange 2010 services are running.


    Best Regards,

    Lynn-Li
    TechNet Community Support


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    Wednesday, November 23, 2016 6:55 AM
    Moderator
  • I am running the below:

    Exchange 2010: Rollup 14 with SP3

    Exchange 2013: with CU14

    I see this error, its doing for one of the DC

    Process w3wp.exe () (PID=6356).  Exchange Active Directory Provider lost contact with domain controller xxxx.xxxx.LAN.  Error was 0x51 (ServerDown) (Active directory response: The LDAP server is unavailable.).  Exchange Active Directory Provider will attempt to reconnect with this domain controller when it is reachable.  

    If i run the command echo %logonserver% and Get-ADServerSettings | fl, its connected to other DC.

    This is happening only for emails going to Exchange 2013 users.

    And its like happening daily once, after i bounce the Topology service it works fine, not able to figure out, i have enabled the logging for the IntraOrg connector, any other suggestions plz.


    mdimthyas

    Saturday, November 26, 2016 5:26 AM
  • Hi

    As per your errors, it looks like the communication between your DC and exchange is incorrect, and name resolution is not properly working.

    Make sure your tcp/ip stack is ok, DNS is fine, check event viewer for more information about issue. once communication between the server is ok you can minimize your problem.

    Kindly click "Mark as Answer" on the post that helps you, this can be beneficial to other community members reading this thread.

    Regards.

    H.shakir

    Saturday, November 26, 2016 6:59 AM
  • Hi

    Are you followed the pre-requisite before installing Exchange 2013? In your exch 2013 server, open command prompt and use 'nslookup' to see what is the default server it is showing. It should be your local dns server. If it is not resolving or showing different then you need to check your gateway and dns settings on the server.

    Second, check the domain controller file replication service for working fine or any warning or errors. 

    Thanks

    Saturday, November 26, 2016 8:08 AM
  • Its resolving fine, it is happening only once in a day, not sure what else i have to check,nothing is showing in connection logs, i enabled login for intra org log, nothing is working.

    We have 13 DC'S, i know one of the DC is having problem. I even forced Exchange to look at local DC but still seeing the problem.


    mdimthyas

    Tuesday, November 29, 2016 4:11 AM
  • I am running the below:

    Exchange 2010: Rollup 14 with SP3

    Exchange 2013: with CU14

    I see this error, its doing for one of the DC

    Process w3wp.exe () (PID=6356).  Exchange Active Directory Provider lost contact with domain controller xxxx.xxxx.LAN.  Error was 0x51 (ServerDown) (Active directory response: The LDAP server is unavailable.).  Exchange Active Directory Provider will attempt to reconnect with this domain controller when it is reachable.  

    If i run the command echo %logonserver% and Get-ADServerSettings | fl, its connected to other DC.

    This is happening only for emails going to Exchange 2013 users.

    And its like happening daily once, after i bounce the Topology service it works fine, not able to figure out, i have enabled the logging for the IntraOrg connector, any other suggestions plz.


    mdimthyas

    Hi,

    You can increase the logging level on the problematic DC with setting the following registry value to 2.

    HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NTDS\Diagnostics\16 LDAP Interface Events

    It will give you more error information, try to find some error messages related to Directory Service.

    And after doing some research, LDAP send queue limits may cause this error event, refer to two documents

    https://technet.microsoft.com/en-us/library/active-directory-maximum-limits-scalability%28v=WS.10%29.aspx?f=255&MSPPError=-2147217396

    http://bill-long.com/2014/03/20/LDAP-send-queue-limits-cause-event-2070-and-2084/

    Note: Microsoft is providing this information as a convenience to you. The sites are not controlled by Microsoft. Microsoft cannot make any representations regarding the quality, safety, or suitability of any software or information found there. Please make sure that you completely understand the risk before retrieving any suggestions from the above link.


    Best Regards,

    Lynn-Li
    TechNet Community Support


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    Tuesday, November 29, 2016 6:26 AM
    Moderator
  • Redirect unreachable Queue mails to EX13 Transport Serivce & monitor whether mails are getting deleivering or getting same error.
    Tuesday, November 29, 2016 4:23 PM
  • Hi, mdimthyas

    How are things going? Have you found something as I suggested above?


    Best Regards,

    Lynn-Li
    TechNet Community Support


    Please remember to mark the replies as answers.
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    Thursday, December 1, 2016 1:27 AM
    Moderator
  • Sorry, could not check it, we had a mail flow issue and was busy tackling it.

    mdimthyas

    Sunday, December 4, 2016 4:13 AM
  • Sorry, could not check it, we had a mail flow issue and was busy tackling it.

    mdimthyas

    Ok, if you have any further problems, please let me know.

    Best Regards,

    Lynn-Li
    TechNet Community Support


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    Monday, December 5, 2016 3:13 AM
    Moderator
  • No luck, i did the registry change, i see error which say, but not sure if its related to it.

    Internal event: The LDAP server returned an error. 

    Daily i have to bounce the Topology service, i have to initiate moves for other users as well now, but thinking as this would cause lot of emails queuing up.


    mdimthyas

    Wednesday, December 28, 2016 4:26 AM
  • Finally, this got resolved, hope it might help someone.

    When I checked, we had 3 DC's in a Site , but one of the DC was in a different physical location and was having some issues.

    Created new Site and moved that DC to new AD Site and also corrected the Subnets and assigned them to the correct site.

    After that not seeing any issue with the emails getting stuck in queue.


    mdimthyas

    Monday, January 16, 2017 8:15 AM
  • Finally, this got resolved, hope it might help someone.

    When I checked, we had 3 DC's in a Site , but one of the DC was in a different physical location and was having some issues.

    Created new Site and moved that DC to new AD Site and also corrected the Subnets and assigned them to the correct site.

    After that not seeing any issue with the emails getting stuck in queue.


    mdimthyas


    Thanks for updates. Glad to hear that it's solved!

    Best Regards,

    Lynn-Li
    TechNet Community Support


    Please remember to mark the replies as answers.
    If you have feedback for TechNet Subscriber Support, contact tnmff@microsoft.com.

    Monday, January 16, 2017 8:38 AM
    Moderator