unusual question -- nk2 file -- contact list

[John]

Whenever I enter the first three letters of a name or
email in the "to:" line in order to send an email in
Outlook, the program suggests a list of possibilities to
choose from. These suggestions do NOT draw from the
Address Book. They are contained in an "nk2" file, which
cannot be opened via Word. I would like to access this
file, as it contains a larger group of name/email contacts
than the formal address book. Does anyone know how this
can be accomplished?

Thanks so much to anyone who can help. Regards.