When our company upgraded to Microsoft Exchange 2000 Server, we used Exmerge to export our mailbox data, formatted the disks, built a new Exchange 2000 server running on Windows 2000 Server, then used Exmerge to import the mailbox data. Now users are getting a lot of Undeliverable messages that include the following text: The e-mail address could not be found. Perhaps the recipient moved to a different e-mail organization, or there was a mistake in the address. Check the address and try again. <myserver.mycompany.com #5.1.0>. The problem primarily happens when a user replies to a premigration message or forwards such a message to an address that was listed in the message. The problem doesn't occur when users manually select the same addresses from the Global Address List (GAL).
My guess is that the clients are pulling old Exchange Server 5.5 addresses. How can I update our Exchange clients to use the new addresses in the new GAL?
My company recently migrated to Exchange 2000 from Exchange 5.5 and ran into the same problem. Your clients are referencing recipient addresses that are left over from your Exchange 5.5 GAL. Even though recipients' SMTP addresses haven't changed, Microsoft Outlook and Exchange see these addresses as different and bounce any new messages that reference premigration threads because the new messages still reference the original GAL entries (e.g., through old X.400 addresses).
For example, suppose that you're a user with an Exchange mailbox on my corporate network, and I begin an email exchange with you today. If tomorrow our IT department uses Exmerge to migrate to Exchange 2000, the Exchange GAL will see your internal address after the migration as being different from what it was when I sent you the message. If tomorrow I use Outlook's Reply function or Reply to All function to reply to your response to my original message, Exchange will send my reply to your old GAL address and the message will bounce.
The only solution I know of is to delete the premigration address from the message thread, then retype the complete address. This action will cause the new GAL to properly identify and expand the address. As you noted, the problem doesn't occur with new messages because the GAL reference for new messages identifies recipients from the current GAL.