Where are the NK2 files stored?

"Vince Averello [MVP-Outlook]" wrote in message
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Look for & delete your NK2 file(s).

"BTuohy" wrote in message
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I would like to purge the drop down and autofill lists for each of the To,
Cc and Bcc combo boxes in a mail form. There are old or incorrect entries
in memory and we would like to start anew.

How is this done?