You must be using an exchange Email account on Microsoft Outlook and that is why you are reading this page. While composing a new Email message have you noticed that when you type the initial letters of the name of a person in the To box, Microsoft outlook automatically suggests you the names and then you simply use the arrow keys or click on the desired name and it comes in the To box. Why does it happen and why does it happen only for those names to which you have sent the mail earlier. It is a kind of auto fill feature in outlook which tries to automatically populate the name of the person in the To box as you type. If you are using outlook in the same domain where your exchange server is located then you would not be prompted by outlook to enter your user name and password but if it is at some other place then it definitely will ask for your exchange username and password. First of all let me tell you that this auto fill feature is the feature of Microsoft Outlook and works locally on your computer. If you change the computer and configure your exchange on the new system then outlook will not auto fill the names you previously have used on the old computer.
Now we understand that the auto fill feature of outlook is profile dependent and computer dependent. This means that the list of recently used names gets stored in the computer somewhere. Logically since this feature is profile dependent so the list should be somewhere in the user profile folders. That is true the list is saved in a file in the user profile and is located in C:\Documents and Setting\Username\Application Data\Microsoft\Outlook in Windows XP and in C:\Users\ Username\Application Data\Microsoft\Outlook in Windows Vista or above. Let is see how we can empty this list if we want.
The file in which the recently used names of Outlook are saved can have any name but the extension would be .nk2. In order to reach and access this file, first of all close Outlook and then open Computer. In computer click on organise and then on Folder options. In folder options click on the View tab and then select Show hidden files and folders. Also please uncheck the box which says Hid Extensions for known file types. Once done close the Folder options window and return back to the main Computer window. Now if you have Windows XP then browse to the “C:\Documents and Setting\Username\Application Data\Microsoft\Outlook” folder and if you have Windows Vista or Windows 7 then browse to the “C:\Users\ Username\Application Data\Microsoft\Outlook” folder. In this folder you will see a file which will have .NK2 as its extension. Right click on this file and select delete. Once the file is deleted open outlook and try writing somebody’s name in the To box of a new mail message and you will see the difference Outlook will now not give you the suggestions. But once you start sending mails a new .NK2 file will get created and it will again start storing the recent names which you used.