Most of you may remember, that in Outlook 2007 and earlier, all autocomplete email addresses were saved in the *.NK2 file, or in even older versions of Outlook they were the *.NICK file.
The NK2 file (or Nickname file) could be easily identified because it was the same name as your Outlook profile. So if your Outlook profile was called “Work Email” the NK2 file was called “Work Email.NK2”.
This made it easy to transfer that autocomplete data to a new profile.
You would create and log in with a new profile, let’s call it “Personal Email”. This would create a blank new NK2 file called “Personal Email.NK2″. Then you could simply delete that NK2 file (I usually renamed it to Personal Email.OLD” – a force of habit). Next, rename “Work Email.NK2” to “Personal Email.NK2”. When you log into your new profile all your auto-complete data was there.
This all changed in Outlook 2010. Outlook 2010 did away with the NK2 file completely and merged all the autocomplete data into the users Exchange Mailbox/PST file. This was great in part as many people often forgot to transfer that NK2 file when they moved to a new computer, or, the autocomplete data was lost in the event of a catastrophic failure, such as a failure of the local hard drive.
The challenge this created for me was that I had a user that owned two Exchange mailboxes which were configured under one profile. They wanted to change which mailbox was their primary/default mailbox. However, both mailboxes had completely separate autocomplete data attached to them and whichever was the default mailbox was the one that populated the autocomplete data in the current Outlook profile. (We were also making a new profile as they were also switching from On-Premise Exchange to Office365 at the same time.) So when I made the secondary mailbox the default/primary in the brand new profile the autocomplete data changed to a much older and undesirable copy.
What I found is that in some form autocomplete data does still exist in your local profile. On a Windows 7 box if you navigate to the RoamCache folder identified below:
You may find one or more files called.
Stream_Autocomplete_<string of numbers and letters>.dat.
This is basically the new cache file for AutoComplete. The string of numbers is likely a SID of some form but where it is referenced (probably the registry) is beyond me.
To figure out which AutoComplete file belonged to which profile I modified the To cache by adding or removing an address. This changed the timestamp on the DAT file. That way I knew which DAT file belonged to which profile. From there I could copy and overwrite the new profile’s autocomplete cache file with the old one. And presto! All autocomplete data in the new profile was from the old profiles primary mailbox.
Hope this helps.