Microsoft Outlook users often noticed that, there is an address auto-complete option which enables them to store and show all email address automatically when they type an address to send mails. It keeps storing every new address while someone send mails to and shows every time while composing any new mail. MS Outlook automatically creates a database file called “Outlook.NK2” at first use of Outlook.
Normally this Database file stored in a hidden system folder and all are need to make that hidden folder visible and the file extension should be visible from the Windows’s folder option. Unless visible this hidden file none can gain access or view the “Outlook.NK2” file. After format C or system drive and reinstall windows, everyone noticed that the auto-complete of email address on MS Outlook 2003 & 2007 is missing.

So, in order to solve this problem all we have to backed up a small database file called Outlook.NK2 before format the system drive and replace the file after windows install into the same location. Just follow the below guide to complete the procedure:
1. you have to make visible hidden files & folder and untick the option "Hide extensions for known file types" from My Computer ->Tools->Folder Option->view.

Then ...
2. Go to C:\Documents and Settings\[User Profile]\Application Data\Microsoft\Outlook (In windows XP, Windows 2000 and Windows 2003 OS)
Or
3. Go to C:\Users\[User Profile]\AppData\Roaming\Microsoft\Outlook (Windows Vista, Windows 7, or Windows server 2008 OS)
4. Copy the "Outlook.NK2" file into a flush drive or any other drive except the drive which you are going to format and install OS (Operating System).

5. After complete installing the OS and Office package just paste that file (outlook.NK2) into the same location mentioned above. Make sure to copy the right file .NK2 file, look carefully for the file extension because there is many other files located into the same folder and may be with the same name. unless make file extension visible from the folder option you can’t determine the exact file type.
Some times in some computer it has been shown that, hidden system folder can not be accessed; this happens due to some virus infection. To get rid from this hassle all have to keep their computer virus and malicious software free, regular check for errors in registry, malware and spyware protection. There is lots of free and commercial softwares are available in the internet for virus guard, registry cleaning, spyware and malware removal.
