Just upgraded the Exchange 2010 to 2013 and everything seems to be functional as expected. However, we started to get some failed logon events on the new Exchange 2013 with the error, "Client not found in Kerberos database: wrong username, or new computer/user account has not replicated to DC yet.". Those accounts are older than 15 years old and of course no longer in our AD. I could not locate them in ADSI either. I don't think there's any devices out there with their credentials trying to connect.
Any suggestion is appreciated!
Thanks
Calvin