While creating a new Outlook profile the other day, I found that in Outlook 2010, the autocomplete cache (the file that stores previously entered destination addresses) is no longer stored in the .NK2 file we all know and love, but instead in a .DAT file that’s supposed to follow the Exchange account (not sure whether this is dependent on the version of Exchange server–the articles I was able to find are kind of sketchy on this functionality, so maybe someone who runs across this blog can fill me in?).
In earlier versions of Office, restoring the autocomplete cache is as simple as copying/renaming the old .NK2 file to match the name of the new Outlook profile. Unfortunately under the “new and improved” system, the .DAT filename no longer matches the profile name, so you need to figure out which .DAT file matches which profile (using timestamps, etc.) before copying the old .DAT file to a new one.
Here’s some additional reading: