Nk2 / Autocomplete - Any way to tell Outlook to NOT save "EXCH" type addresses and only "SMTP" addresses

Have a client with mostly Office 2007 (won't upgrade to 10 or 13 yet).  So, still using NK2 files.  I'm pretty sure that somewhere/someone in the organization has old/invalid Exchange addresses in their NK2 for a couple users.  That "someone" (or multiple "someones") with the old/invalid Exchange addresses appears to be polluting other user NK2s when they send out emails.  These users with the "polluted" NK2 file are receiving the following bounce error even after multiple attempts at deleting the bad entries:  550 5.1.1 RESOLVER.ADR.ExRecipNotFound  
The organization is large enough that I can't go to each user(s) and NK2 file to find and "x" (delete) the entry when found.  Turning off the NK2 ("Autocomplete") function entirely would not be a popular option.  

So, my question boils down to:  Is there a way to tell Outlook to store ONLY external smtp addresses in the NK2 and NOT internal exchange addresses?

A secondary question is:  Is this even an NK2 issue or could these invalid Exchange addresses be coming from something like "Suggested Contacts?"

Thanks in advance.