One attendee had this problem:

We use Outlook 2003 and my users aren't very good at adding email addresses to the Contacts folder and rely heavily on the autocomplete cache, but it gets replaced often.

First, I'll explain how the autocomplete cache works. The autocomplete cache is also known as the nickname cache, and is stored as a hidden file in C:\Documents and Settings\username\Application Data\Microsoft\Outlook\<profile_name>.NK2 if you use Outlook 2002/2003. It has a limit of 1000 of the most recently used addresses, and new addresses are not added to it until you end the current Outlook session. There is a registry key you can edit to control the size of the nickname cache in Outlook2002, but it doesn't work with Outlook 2003.

Managing the nickname cache is easy. If you have a mistyped address in your cache you can use the arrow keys to select the address and press Delete to remove it. Or you can delete the existing NK2 file to completely clear the cache and start with a clean cache file.

If the users are losing addresses of people they recently replied to, it's because Outlook crashes or does not close properly and the changes aren't written to the NK2 file. The existing *.NK2 shouldn't be replaced by a clean *.NK2 if this happens, but new addresses you've sent mail to, or replied to won't be saved to the file. Less used addresses are replaced by new addresses when the NK2 contains 1000 addresses, but if something is corrupt, Outlook replaces the current NK2 with a new, clean one. We don't know what causes it to become corrupt, but we suspect a large number of addresses in the cache is part of the problem.

Microsoft doesn't provide a tool to edit the nickname cache, but if you need to view or edit the NK2 file, a third party utility called Ingressor Desktop (formerly Owtlook) is available. This $35/user tool allows you to edit the NK2, capture the addresses and create contacts, or populate it with frequently used addresses. Owtlook is especially useful for corporations that need to capture all addresses employees correspond with.

If you're using the autocomplete cache as your address book because it's too much effort to right click on an address and save it as a new Contact, you should use a utility that creates contacts from all addresses you reply to, as the autocomplete cache is not a good substitute for storing addresses in contacts. You'll find a list of utilities on Slipstick at http://www.slipstick.com/addins/contacts.htm#data, or use Owtlook to collect and save the addresses. Microsoft also has a file in their knowledge base entitled, " Reduce the Number of Names in the Nickname Cache (Outlook 2002)" at http://support.microsoft.com/?kbid=293032 that addresses this issue as well.

Diane Poremsky is the president of CDOLive LLC and a Microsoft Outlook MVP. She's author of Teach Yourself Outlook 2003 in 24 Hours (Sam's, 2003) and coauthor of OneNote 2003 for Windows (Visual QuickStart Guide). For questions or suggestions for future columns, write her at outlook@cdolive.com.