When you type a name into the To or CC field in Outlook, the list of addresses that pops up is not generated from your address book. It is the Autocomplete cache and is stored in a separate file called "<name_of_outlook_profile>.nk2". As you type new addresses it updates this file with up to 1000 addresses.

This nk2 file can usually be found under C:\Documents and Settings\<username>\Application Data\Microsoft\Outlook.

For each profile you get a new .nk2 file. If your profile name is "Outlook" then while logged in to that profile addresses get added to the "Outlook.nk2" file.

The .nk2 file cannot be edited directly, but you can easily transfer it between profiles and delete entries from it. 

Transfer a previous nk2 file to a new profile

if you setup a new profile in outlook you may want to keep the cache from the old profile.

Simply create the new profile, open outlook in the new profile, then exit.

Then browse to C:\Documents and Settings\<username>\Application Data\Microsoft\Outlook. (replace <username> with your username)

Copy the old .nk2 file from your old profile to a new file. Then rename it so it has the same name as your new profile.

When you start outlook back up you should have your cache back.

Remove entries from the Autocomplete Cache

You can remove entries from the autocomplete cache in two ways:

1. Close Outlook. Delete the .nk2 file for that profile. Restart Outlook. Note: this will remove all entries and basically start from scratch.

2. Remove individual entries. Sometimes dud or old addresses get cached and you may want to exclude them. Follow the procedure below to remove them.

Open a new message. Begin typing an address for the cache list to appear. Highlight the incorrect entry in the drop down box using the arrow keys and press the Delete key on your keyboard. The entry will be removed from the autocomplete cache.