All,I have been trying to figure this out for hours! We just migrated to 2007 and decommissioned 2000. ALL mailboxes were moved over to 2007, everyone's email works except one person. They appear in the management piece as having a mailbox as well as items in it, but when you try and send something to that person you get this: IMCEAEX-_O=MyDomain_OU=First+20Administrative+20Group_cn=Recipients_cn=user@mydomain.org #550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ## It appears as though the lookup is still pointing to the Exchange 2000 Box, I have tried looking in active directory to change it and I can't. And I tried viewing properties in Exchange Management Console (where it says Exchange 2003 Mailbox) but it gives me this error: "The operation could not be performed because object ..... could not be found on domain controller "dc1".Any help would be much appreciated!!!!

Hi, t's difficult to say what's going on with just a few information. But, here is something that can help you. Compare a good mailbox and the bad mailbox user, dump the object the from the active directory. Use the command ldifde.exe to dump the account of each user, and then compare the difference between them using windiff utility. ldifde -f <outputfile.ldf> -s <DC> -d <dn of the user account>

I think I figured it out, I used the Mailbox Recovery Center in Exchange 2003 to re-associate the email box in Active Directory (thanks to a KB article from Microsoft). I could not find the proper tool in Exchange 2007 or Exchange 2000, so Exchange 2003's System Manager saved the day!

What was the KB article number for the re-associate of the mailbox. I am having the same issue

I can't remember the KB article-- but I think this was one of the links I used: (it was a crazy night) http://technet.microsoft.com/en-us/library/aa996202.aspx