Users started getting a replay message containing “550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found” when sending internal e-mail to a specific user. After som research I found out that this user first was created in the Active Directory & Exchange and then delete a while ago. Recently the same user has been created. When I understood that I came to think about if the problem was in the clients auto-complete cache in Outlook. You can easily empty the cache in Outlook 2010 (options/mail/send messages/empty auto-complete list). But I wanted to edit the list to remove the specific users e-mail adress.

I found this great application called NK2Edit.

The file that contains the auto-complete cache is:
C:\Users\%username%\AppData\Local\Microsoft\Outlook\RoamCache\Stream_Autocomplete*.dat.

Just download and run NK2Edit and it will automatically open C:\Users\%username%\AppData\Local\Microsoft\Outlook\RoamCache\Stream_Autocomplete*.dat. Edit and save the auto-complete list.

Remember to exit Outlook 2010 before you save Stream_Autocomplete*.dat.