Outlook CACHE causing NDR when recreating mailbox during migration

No matter what you do, some mailboxes just fail to move during the migration. My last resort would be to blow the mailbox away on the legacy server, re-create on the new server, then import the PST back to the new mailbox. However, this would cause another headache afterward: other internal users will get NDR when sending emails to the new mailbox due to the Outlook cache. Below is a quick way to fix it without touching each Outlook client to manually delete the cached name:

1. Write down the LegacyExchangeDN value before removing the mailbox. You can do this either using ADSIEDIT.MSC or running the following Cmdlet from EMS:

Get-Mailbox AWang | fl LegacyExchangeDN

2. After you recreate the mailbox on the new server, create a new X500 address for the user and put in the LegacyExchagneDN recorded in step 1.