I migrated a linked mailbox from Exchange 2007 to 2013 today and the user was unable to open their outlook profile or access their mailbox via OWA. I disabled their mailbox, then connected to it again as a user mailbox to their AD account. They were then able to access their mailbox via Outlook and OWA. However, now when other users in the organization enter their name in Outlook or select it from the GAL. Outlook mail tips says "this e-mail message cannot be delivered to <recipient> because the e-mail address is no longer valid." I've tried adding back their X500 address, deleting them from my auto-complete cache with no luck. All other users in my Exchange 2007 environment are user mailboxes so it's not a concern, but for some reason this was a linked mailbox even though they were never part of another forest. Any suggestions on how to get rid of this Outlook message? They're still receiving email when you send.