Outlook 2007 improves user productivity by caching the most recently used e-mail addresses entered in the TO:, CC:, and BCC: fields when messages are sent. This cache is stored in an AutoComplete file with the extension .NK2 located in the user’s profile, for example in Windows Vista it would be:
As the user types an address, the cache items matching the letters typed are displayed in a dropdown box [See Figure 1]. The user can navigate through the cached items with the arrow keys and select the desired recipient if it is present. By the same manner, the user can delete individual entries in the cache as well. The AutoComplete file handles up 1000 entries and stores more than just addresses. Among its content resides X.500 directory information, X.509 PKI certificate data, and auto-resolution information as well.
If there are many addresses in the NK2 file that are no longer desired or the file is not providing information correctly through possible corruption, the file can be deleted. Outlook will create a new one with no entries next time that profile is opened as outlined in Microsoft KB article 287623. The cache will build again as the user sends mail.
Not everyone may want this feature. The added convenience may increase the potential to send confidential content to an unintended recipient. AutoComplete is easily toggled on or off through Outlook. Navigate to Tools | Options | E-mail Options | Advanced E-mail Options. To disable AutoComplete, clear the checkbox beside the option to Automatic Name Checking and Suggest names while completing To, Cc and Bcc fields options [See Figure 2]. The former checks address books and the cache to resolve recipients while the latter is responsible for displaying the dropdown box for AutoComplete.
While intended as a productivity feature of Outlook, some have grown to depend on the AutoComplete cache almost as an address book. There are third party applications that can parse the .NK2 file and present its contents in an interface through which users can administer their AutoComplete file. Ingressor and NK2View are two examples of Outlook AutoComplete management tools.
For more tips, visit a collection of popular Outlook help articles on the Outlook tips page.
This post is part of the series: Microsoft Office Outlook 2007 Tips
A series of Tips and Tricks for working with Microsoft Outlook 2007 both as a user and an administrator.
- New E-mail Account Configuration in Microsoft Outlook: Tip #1
- Use AutoComplete “Nickname” Cache in Outlook: Tip #2
- Configure Outlook Custom Message Views: Tip #3
- How to Configure RSS Feeds in Outlook: Tip #4
- Tip #5 - Making Changes to the Custom Dictionary in Microsoft Outlook 2007
- Tip #6 - Configure Outlook Autosave Settings
- Microsoft Outlook Keyboard Shortcuts: Tip #7
- Microsoft Outlook 2007 Tip #8 - Outlook.exe Startup Switches
- Microsoft Outlook Instant Messenger Addons: #9
- Tip #10 - Using Outlook 2007 to Access GMail
- Showing Full Message Headers in Microsoft Outlook 2007: Tip #11
- How to Re-Send an E-mail Message in Outlook: Tip #12
- How to View Animated GIFs Embedded in an E-mail in Microsoft Outlook 2007: Tip #13
- Telling Outlook How to Handle Messages: Tip #14
- Microsoft Outlook 2007 Tip #15 - How to Color Code the Task List in the To Do Bar
- Tip #16 - Importing from Incredimail to Microsoft Outlook 2007
- Viewing Multiple Outlook Calendars: Tip #17
- Removing Cancelled Future Appointments in Microsoft Outlook 2007: Tip #18
- Tip #19: How to Create New Outlook E-mail from the Command Line
- How to Configure Outlook AutoArchiving: Tip #20
- Using Custom Categories in Microsoft Outlook 2007: Tip #21
- How to Manage Outlook Add-ins: Tip #21
- Microsoft Outlook 2007 Tip #23 - Attachment Previewing Options