We recently completed an exchange Migration/merger. Some users are now getting 550 5.1.1 RESOLVER.ADR.ExRecipNotFound errors. They do not get these when using OWA. We have tried deleting their NK2 files but this did not work. If they get an error for a person, have that person send them an email and then they reply the issue goes away for that email address.
Let me know if you need more information.
We have 2 AD forests with a 2 way trust.
Forest 1 - Coakley
Forest 2 - Records
The Coakley forest contains users and the old exchange 2003 server
The Records forest contains users and the exchange 2010 server. The records users have been using this server for several months. The Coakley forest users mailboxes have just been migrated.
The Coakley forest users mailboxes are linked mailboxes, the records forest users mailboxes are normal User Mailboxes.