Cannot Reply To Old Emails Or Modify Old Calendar Items After PST Mail Migration

[Today's post comes to us courtesy of Wayne McIntyre and Justin Crosby]

Note: This article has you make changes to Active Directory.  Before doing so be sure to make a complete backup.

After a mail migration to a new domain/Exchange organization using Exmerge, you will lose the ability to reply to old email and modify old calendar items. The reason this occurs is because the message is stored with x500 address from the old domain. In order to correct this you need to add this old X500 address as proxy address for the user account in Active Directory in the new domain.

You will need to build the user's new X500 proxyAddress from the the user's LegacyDN attribute from the old domain.  To get this attribute, launch ADSIEDIT.msc on the old domain controller and open the properties of the user account.  Locate the legacyExchangeDN value and copy it to notepad.


Next you must prefix "X500:" (without quotes) to the value in notepad.


Old/Source legacyExchangeDN = /o=TAILSPINTOYS/ou=first administrative group/cn=Recipients/cn=test2

New proxyAddresses = X500:/o=TAILSPINTOYS/ou=first administrative group/cn=Recipients/cn=test2

Note: In our example TailspinToys is the Exchange Org and Test2 is the user's alias. 

On the new domain controller edit the proxyAddresses attribute of the migrated user and add your modified X500 value to the proxyAddresses attribute.  Do Not delete the SMTP: address.  Do Not modify the legacyExchangeDN value on the new domain.


Modifying the value in bulk

If you have a lot of users and want to do this in bulk you can use the tool, which you can download from

1. Launch ADModify and select Modify Attributes.


2. Select your domain in the Domain List and your domain controller in the Domain Controller list and hit the green arrow button.


3. Traverse thru your domain tree until you locate the OU which contains the migrated users and select Add to List.

4. Highlight the users from that OU that you wish to modify then click Next.


5. On the Custom tab, check the boxes for "Make a customized attribute modification" and “Multivalued Append”.   Enter the values as follows then click Go!.

Note: You must modify the values accordingly, with the legacyExchangeDN you retrieved from the source domain.  Do not copy and paste the values from this blog post.

Attribute Name: proxyAddresses

Attribute Value: X500:/o=YourOrgHere/ou=first administrative group/cn=Recipients/cn=%’mailNickname’%


Note: In some cases your mailnickname may have changed, if this is the case you will not be able to do the bulk edit and will have to manually add the x500 address for those users.