I have had to deal with this issue for a few smaller networks, but I now have to find a way to automate this issue as I am not about to do the same for 100 Users :)
We are setting up a new AD Domain, and manually migrating User Profiles, setting up new Exchange Mailboxes and importing in from Exmerged PST.
Outlook 2010 and Exchange 2010 is being used, and data is coming from Outlook 2003 and Exchange 2003. We will also be migrating Nickname-Cache into Outlook 2010.
Issue is that when a User goes to send to an internal User from their NK2 (Suggested Contacts) in Outlook they will receive a NDR as I believe the entry will be looking for old distinguished domain name or email address.
Is there a way I can ensure this does not occur? Like editing new AD User accounts to include legacy user accounts?