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errors after answering old emails after migration to office 365 from owned exchange 2007

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we HAD internal exchange 2007

we switched to office 365


after 2 days of searching (with proper exchange specialists) to connect for the cut over, we decided to export all mails, contacts etc to pst files and imported them in office 365


the problem:

when answering old email messages to our internal users, we get errors


bericht kan niet worden bezorgd bij de volgende geadresseerden of groepen:

'Cindy Huygh'

Het door u ingevoerde e-mailadres is niet gevonden. Controleer het e-mailadres
van de geadresseerde en probeer het bericht opnieuw te verzenden. Als het
probleem blijft bestaan, neemt u contact op met de helpdesk.

clicking on the name link gives


wat to do about it??

kind regards






All Replies
  • Hello Eric,

    I have translated the NDR into English through translation tool, if some inaccurate words, please correct it.
    “your message can not be delivered to the following recipients or groups:
    "Cindy Huygh"
    The email address you entered was not found. Check the e-mail recipient of the message and try sending again. If the  problem persists, contact the helpdesk. “

    It’s an expected behavior when you migrate email through PST file and try replying old email. After the PST migration, the old email contains the old sender’s identity (legacyExchangeDN), but this identity is not applied to the sender in Office 365 cause the user account is different although the email address, name or other attributes remain the same. So when you reply this email, Office 365 cannot deliver this email to the old identity.

    You can either use the Office 365 migration tool to perform the migration job again, or you can export the legacyExchangeDN of on-premise Exchange 2007 user and add it as proxy address for the corresponding Office 365 user account as x500 address.

    To get the old legacyExchangeDN, you can use on-premise Exchange Management Shell, run Get-Mailbox user | FL legacyExchangeDN to get this attribute.

    To add it to proxy address for Office 365 user, you can connect to Exchange Online through Exchange 2010 EMC, choose the corresponding mailbox user, go to properties, under Email Address, click add, paste the old legacyExchangeDN and set type as x500.

    Lester Zhang

  • hi

    i managed to get into the old server and run the command

    this is the response:

    LegacyExchangeDN : /o=VVT/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn


    1.  what piece should i use?

    2.  i went to as administrator of our office 365 - manage exchange

    there, when i want to add an alias on a existing mailbox, i do not see a x500 type

    i can only add the first part before the @ sign and a dropdown with our several domain names

    how to do is??



  • Hello Eric,

    The part after the LegacyExchangeDN : is what we need.

    To set the email addresses/proxy addresses, you can either use Exchange Management Console for Exchange 2010 or use PowerShell set. Exchange Control Panel is not capable for this job.

    If you do not have Exchange 2010 EMC on site, you can use PowerShell to finish this job. You may check the following steps for reference.

    1), Using administrator account to connect to Exchange Online through PowerShell,
    2), Run $user=Get-Mailbox username,
    3), Run $user.EmailAddresses+=”X500:/o=VVT/ou=Exchange Administrative Group (FYDIBOHF23SPDLT)/cn=Recipients/cn=nadine”,
    4), Run Set-Mailbox username –EmailAddresses $user.EmailAddresses,
    5), Run Get-Mailbox username | FL emailaddresses to check if the address has been added.

    Lester Zhang

  • Hi Eric,

    How is the thing going? Is there any update of this issue?

    Lester Zhang

  • Excellent Zhnag. This solved my problem.

    However, there is typo error in your 3rd line. Need to remove the space after "X500:"

    It rocks!! Thanks..

  • Hi,

    Appreciate your response and provide correction. I have corrected the typo in the original post.

    If you have any other questions or concerns, please do not hesitate to contact us.

    Lester Zhang

  • hi

    first, i tried without succes

    now perfect, after correction of the typo error

    thx a lot

  • it works, after the typo error

    thanks a lot

  • how we can change X500 if we entered wrong info first time. I tried to renter but it does not allow me. I am using stand alone environment of office 365, NO AD synch or hybrid deployment.

  • if you do not know your LegacyExchangeDN because you do not have Aministrator access to the old exchange server (ie. you only have the PST files and no admin access, such as with Godaddy Hosted Exchange), you can still figure it out from the PST file.

    Open the PST file in an Outlook 2010 (File tab, Open, Open data file) and then find a message from or to each of your old users (you may need to use more than one of the PST files to get all the users).  

    Open the existing message from the old server.  Hover over the address of the user (in From: or whatever field they appear in) and a pale yellow tooltip will appear in Outlook 2010 showing the user's X500 From address (it will look like: /O=EX1/OU=EXCHANGE ADMINISTRATIVE GROUP (FYDIBOHF23SPDLT)/CN=RECIPIENTS/CN=USERNAME ) but you will only see the left hand side of it, the rest will be cut off with an elipsis.  But, you can then right click over the portion that is shown and "Copy Name" and your clipboard will then contain the LegacyExchangeDN.   

    Simply add "X500:    before it and "   after it and you have your PowerShell value: e.g.   


  • What about if we came over from Google Apps?  It's bouncing for ALL users in old emails --- not all of the users are even part of my domain either on O365 or GApps.