The LegacyExchangeDN is an important value if you want to do pain-free user migrations between Exchange environments. You can avoid a lot of user requests and problems with NDRs (Non-delivery reports) during migration if you think about it before.
Introductory information described in Jamie McKillop's article, NDRs and the legacyExchangeDN. So in this article I want to show you one possible way how to save that important information.
Let's imagine a complex example: migration between different forests and email domains.
Two forests: ex2003.com and ex2010.com.
Two Exchange organizations: Exchange 2003 (the old one) and Exchange 2010 (the new one.
Three mailboxes: A, B and C, which migrated from the Exchange 2003 to Exchange 2010 (by any means).
After migration of the mailboxes you should save the old SMTP address and old legacyExchangeDN as X500 addresses.
But for automation of process I recommend using a script.
Notes for the script:
First of all you should collect all information about the email and legacyExcahngeDN from the source system (the "Exchange 2003" organization in our case) into a CSV file.
In the case of Exchange 2007 (instead of Exchange 2003) as source system you can upgrade the script to taking legacyExchangeDN automatically from the target AD (if mailboxes still exist).
You can run the script as many times as you need (it checks for duplicates).
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